<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2023 Workiva-->
<!--r:ae4f0363-5d72-42a9-93e9-2c818ee6cad3,g:d0908303-95e9-48ce-8f74-838c7d9675e9-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.gentex.com/role/UNAUDITEDCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSINVESTMENT" xlink:type="simple" xlink:href="gntx-20230930.xsd#UNAUDITEDCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSINVESTMENT"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/UNAUDITEDCONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSINVESTMENT" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_036caab2-f4f8-4455-8428-032fd0855d0f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_036caab2-f4f8-4455-8428-032fd0855d0f" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_34fad20d-ca9c-4019-ab57-fd55cc797973" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_34fad20d-ca9c-4019-ab57-fd55cc797973" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_5ed9fcf3-9f0d-4809-9b43-535b2124e723" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_StockholdersEquity_5ed9fcf3-9f0d-4809-9b43-535b2124e723" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_cddb8646-48f2-4c44-8450-daa8f018911d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_cddb8646-48f2-4c44-8450-daa8f018911d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_301ab605-b7f3-4809-94d2-8fbb32699429" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_301ab605-b7f3-4809-94d2-8fbb32699429" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_5cf56fc2-e651-46bb-80a1-9ac60b6b33d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_5cf56fc2-e651-46bb-80a1-9ac60b6b33d0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_3fa3a9b0-af2b-49c6-8691-c226a531964d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_3fa3a9b0-af2b-49c6-8691-c226a531964d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodShares_3e7e607e-5e4c-4e5a-903c-a8fedaefbb33" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodShares_3e7e607e-5e4c-4e5a-903c-a8fedaefbb33" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedDuringPeriodValue_9458a540-857f-4482-b18b-60fb44e92ebc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockRepurchasedDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_StockRepurchasedDuringPeriodValue_9458a540-857f-4482-b18b-60fb44e92ebc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_a6a1eaf2-88f0-4b5a-8fe7-8820afba7e2f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_a6a1eaf2-88f0-4b5a-8fe7-8820afba7e2f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsCommonStockCash_d36483e8-7c58-4ee4-a4ed-96f82eab59e3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsCommonStockCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_DividendsCommonStockCash_d36483e8-7c58-4ee4-a4ed-96f82eab59e3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_ae65e437-acfd-469b-bfe6-a8afee25f6b8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_NetIncomeLoss_ae65e437-acfd-469b-bfe6-a8afee25f6b8" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_727ddc92-b7d6-4669-8c73-20c5e78c2bc3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_6e140214-0581-4b46-ad5f-d29306e656ff" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_727ddc92-b7d6-4669-8c73-20c5e78c2bc3" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_1b624551-e01c-4c45-9b0b-0f615cb8d675" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_dc145c01-c819-4ee7-8aeb-663e2456f325" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_7b619de4-d87f-4614-ad35-93162f65cbfa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_036caab2-f4f8-4455-8428-032fd0855d0f" xlink:to="loc_us-gaap_StatementTable_7b619de4-d87f-4614-ad35-93162f65cbfa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_00a76a8d-7c2a-4736-8f74-f72be3089614" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_7b619de4-d87f-4614-ad35-93162f65cbfa" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_00a76a8d-7c2a-4736-8f74-f72be3089614" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_00a76a8d-7c2a-4736-8f74-f72be3089614_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_00a76a8d-7c2a-4736-8f74-f72be3089614" xlink:to="loc_us-gaap_EquityComponentDomain_00a76a8d-7c2a-4736-8f74-f72be3089614_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2e8c8436-4279-4215-a44a-3b1858fdac28" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_00a76a8d-7c2a-4736-8f74-f72be3089614" xlink:to="loc_us-gaap_EquityComponentDomain_2e8c8436-4279-4215-a44a-3b1858fdac28" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_001e9276-fba6-4efe-85a3-c3917d30cc27" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2e8c8436-4279-4215-a44a-3b1858fdac28" xlink:to="loc_us-gaap_CommonStockMember_001e9276-fba6-4efe-85a3-c3917d30cc27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_d1861bc7-3f68-4d7d-a102-d2f66d4775b9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2e8c8436-4279-4215-a44a-3b1858fdac28" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_d1861bc7-3f68-4d7d-a102-d2f66d4775b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_314e8baa-7d8f-4746-8218-7b1026e018b4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2e8c8436-4279-4215-a44a-3b1858fdac28" xlink:to="loc_us-gaap_RetainedEarningsMember_314e8baa-7d8f-4746-8218-7b1026e018b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_4d7ca804-6ce8-4b68-8527-48b043484cd5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2e8c8436-4279-4215-a44a-3b1858fdac28" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_4d7ca804-6ce8-4b68-8527-48b043484cd5" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsNarrativeDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#GoodwillandOtherIntangibleAssetsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_8c568a69-a8b3-4d32-97ed-25ecf1f3a1a2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_Goodwill_8c568a69-a8b3-4d32-97ed-25ecf1f3a1a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAcquiredDuringPeriod_dff7f61a-1348-4285-96be-9211371cc03c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GoodwillAcquiredDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_GoodwillAcquiredDuringPeriod_dff7f61a-1348-4285-96be-9211371cc03c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_fe9d17f0-47c5-478d-9ade-6e29a79b2e75" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_fe9d17f0-47c5-478d-9ade-6e29a79b2e75" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_51391dcc-280b-4549-a2f0-0e821f0381f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_51391dcc-280b-4549-a2f0-0e821f0381f3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_cca5fdc9-aabe-4a84-be92-9fc1ff4406b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_cca5fdc9-aabe-4a84-be92-9fc1ff4406b3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_25663d5a-7f92-4022-ae7f-57a97220661e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_25663d5a-7f92-4022-ae7f-57a97220661e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_5b1135b1-8fe2-48c0-88b9-c8e5bb71e4ec" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_5b1135b1-8fe2-48c0-88b9-c8e5bb71e4ec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_734ad672-a77c-458f-aea6-8294fa0e248a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_734ad672-a77c-458f-aea6-8294fa0e248a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a4c8e5fa-a5b3-4525-a4d2-b2737bfe955e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_0865ddfc-ae32-4a79-bf90-d0a2cb47fd27" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a4c8e5fa-a5b3-4525-a4d2-b2737bfe955e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_339d7a94-d329-410a-8210-c65f5176d44d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a4c8e5fa-a5b3-4525-a4d2-b2737bfe955e" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_339d7a94-d329-410a-8210-c65f5176d44d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_339d7a94-d329-410a-8210-c65f5176d44d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_339d7a94-d329-410a-8210-c65f5176d44d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_339d7a94-d329-410a-8210-c65f5176d44d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0036f2c9-3617-490e-b550-a0b4d9aa4a74" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_339d7a94-d329-410a-8210-c65f5176d44d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0036f2c9-3617-490e-b550-a0b4d9aa4a74" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_HomeLinkMember_f9d25a7d-c9f3-469f-9a18-9e5a520613ca" xlink:href="gntx-20230930.xsd#gntx_HomeLinkMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0036f2c9-3617-490e-b550-a0b4d9aa4a74" xlink:to="loc_gntx_HomeLinkMember_f9d25a7d-c9f3-469f-9a18-9e5a520613ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_VaporsensIncMember_5bab5f1a-8f82-4e87-8314-843697d60ef6" xlink:href="gntx-20230930.xsd#gntx_VaporsensIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0036f2c9-3617-490e-b550-a0b4d9aa4a74" xlink:to="loc_gntx_VaporsensIncMember_5bab5f1a-8f82-4e87-8314-843697d60ef6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AirCraftGlassMember_e88f097e-d574-47ea-b3f2-abc6ceddfb4f" xlink:href="gntx-20230930.xsd#gntx_AirCraftGlassMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0036f2c9-3617-490e-b550-a0b4d9aa4a74" xlink:to="loc_gntx_AirCraftGlassMember_e88f097e-d574-47ea-b3f2-abc6ceddfb4f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ArgilIncMember_701155f5-5c84-4ce4-a39e-8a4a1090e41b" xlink:href="gntx-20230930.xsd#gntx_ArgilIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0036f2c9-3617-490e-b550-a0b4d9aa4a74" xlink:to="loc_gntx_ArgilIncMember_701155f5-5c84-4ce4-a39e-8a4a1090e41b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_GuardianOpticalTechnologiesMember_63794d27-5eed-401b-b780-3a0f74c0f426" xlink:href="gntx-20230930.xsd#gntx_GuardianOpticalTechnologiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0036f2c9-3617-490e-b550-a0b4d9aa4a74" xlink:to="loc_gntx_GuardianOpticalTechnologiesMember_63794d27-5eed-401b-b780-3a0f74c0f426" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1142c957-9d8b-437f-ae2b-5df0641a29b9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_a4c8e5fa-a5b3-4525-a4d2-b2737bfe955e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1142c957-9d8b-437f-ae2b-5df0641a29b9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1142c957-9d8b-437f-ae2b-5df0641a29b9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1142c957-9d8b-437f-ae2b-5df0641a29b9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1142c957-9d8b-437f-ae2b-5df0641a29b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a81e04f9-402f-4851-be45-04d0aa5b17dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1142c957-9d8b-437f-ae2b-5df0641a29b9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a81e04f9-402f-4851-be45-04d0aa5b17dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PatentsAndOtherIntangibleAssetsMember_3a4e6259-5661-4c65-9b4f-ccc95a134e74" xlink:href="gntx-20230930.xsd#gntx_PatentsAndOtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a81e04f9-402f-4851-be45-04d0aa5b17dc" xlink:to="loc_gntx_PatentsAndOtherIntangibleAssetsMember_3a4e6259-5661-4c65-9b4f-ccc95a134e74" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#GoodwillandOtherIntangibleAssetsScheduleofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/GoodwillandOtherIntangibleAssetsScheduleofIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_862ea650-bf59-4b93-b084-46257897ee55" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_862ea650-bf59-4b93-b084-46257897ee55" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_f0c44475-7455-4575-b826-518f32b2cf71" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_f0c44475-7455-4575-b826-518f32b2cf71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_5abd4663-f6b5-4fc0-96fd-6a6c9b00a801" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_5abd4663-f6b5-4fc0-96fd-6a6c9b00a801" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_5899e01d-4e53-45be-8e51-d6842fb9bb63" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_5899e01d-4e53-45be-8e51-d6842fb9bb63" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_528677ac-14fd-4662-9157-a385c9dd06f0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_528677ac-14fd-4662-9157-a385c9dd06f0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_d5cb0794-26c0-47d2-8f8c-8b8b9c0abc51" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_d5cb0794-26c0-47d2-8f8c-8b8b9c0abc51" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_bd74952c-5c44-48e4-858c-478ea19a195a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_fd075f89-f2e3-4a97-a280-592d5b42d6fe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_fd075f89-f2e3-4a97-a280-592d5b42d6fe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_IntangiblePatentsAndAssetsGrossExcludingGoodwill_1ab1fae9-11b2-4d43-8b8a-d95dc23d60a1" xlink:href="gntx-20230930.xsd#gntx_IntangiblePatentsAndAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_gntx_IntangiblePatentsAndAssetsGrossExcludingGoodwill_1ab1fae9-11b2-4d43-8b8a-d95dc23d60a1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_FiniteLivedIntangiblePatentsAndAssetsAccumulatedAmortization_2f3fe5d3-978e-4b82-b20c-0d7d025e1b20" xlink:href="gntx-20230930.xsd#gntx_FiniteLivedIntangiblePatentsAndAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_gntx_FiniteLivedIntangiblePatentsAndAssetsAccumulatedAmortization_2f3fe5d3-978e-4b82-b20c-0d7d025e1b20" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_IntangiblePatentsAndAssetsNetExcludingGoodwill_396c70aa-9bab-4e94-99ae-e5a7ecb01f4e" xlink:href="gntx-20230930.xsd#gntx_IntangiblePatentsAndAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_gntx_IntangiblePatentsAndAssetsNetExcludingGoodwill_396c70aa-9bab-4e94-99ae-e5a7ecb01f4e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_fb349c82-636b-48c2-9265-3e0ba2047a62" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_7bf2adaf-8750-4661-8d69-df5ab78b7475" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_fb349c82-636b-48c2-9265-3e0ba2047a62" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_75cf9192-2113-41c4-beaf-0e66d6387188" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_fb349c82-636b-48c2-9265-3e0ba2047a62" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_75cf9192-2113-41c4-beaf-0e66d6387188" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_75cf9192-2113-41c4-beaf-0e66d6387188_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_75cf9192-2113-41c4-beaf-0e66d6387188" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_75cf9192-2113-41c4-beaf-0e66d6387188_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f5fef33e-1243-48e2-8ed4-45cf7481928e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_75cf9192-2113-41c4-beaf-0e66d6387188" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f5fef33e-1243-48e2-8ed4-45cf7481928e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentsMember_201feb5c-a6e6-48b4-8c69-99dc13cf55b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f5fef33e-1243-48e2-8ed4-45cf7481928e" xlink:to="loc_us-gaap_PatentsMember_201feb5c-a6e6-48b4-8c69-99dc13cf55b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_b4c15dcd-69cf-42c2-b6a4-a5351453df9f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f5fef33e-1243-48e2-8ed4-45cf7481928e" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_b4c15dcd-69cf-42c2-b6a4-a5351453df9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerContractsMember_cd903243-bc62-47e3-97d3-abe81f3129e4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CustomerContractsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f5fef33e-1243-48e2-8ed4-45cf7481928e" xlink:to="loc_us-gaap_CustomerContractsMember_cd903243-bc62-47e3-97d3-abe81f3129e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_ce95b98a-5444-48dc-abf5-087c55b87883" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f5fef33e-1243-48e2-8ed4-45cf7481928e" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_ce95b98a-5444-48dc-abf5-087c55b87883" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PatentsAndOtherIntangibleAssetsMember_4e388a25-6ea1-49c2-b22e-6e8a66c14dd2" xlink:href="gntx-20230930.xsd#gntx_PatentsAndOtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f5fef33e-1243-48e2-8ed4-45cf7481928e" xlink:to="loc_gntx_PatentsAndOtherIntangibleAssetsMember_4e388a25-6ea1-49c2-b22e-6e8a66c14dd2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_15359a2a-1e5c-465c-a09f-56acd34153ca" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_fb349c82-636b-48c2-9265-3e0ba2047a62" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_15359a2a-1e5c-465c-a09f-56acd34153ca" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_15359a2a-1e5c-465c-a09f-56acd34153ca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_15359a2a-1e5c-465c-a09f-56acd34153ca" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_15359a2a-1e5c-465c-a09f-56acd34153ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1f545240-7349-42a3-8684-dd0664ba3890" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_15359a2a-1e5c-465c-a09f-56acd34153ca" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1f545240-7349-42a3-8684-dd0664ba3890" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksAndTradeNamesMember_d46812a2-1648-46e9-a12e-3fbedbe2e7db" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TrademarksAndTradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1f545240-7349-42a3-8684-dd0664ba3890" xlink:to="loc_us-gaap_TrademarksAndTradeNamesMember_d46812a2-1648-46e9-a12e-3fbedbe2e7db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicensingAgreementsMember_46bfc229-ea41-48c6-b907-e1aa9df65c85" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LicensingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1f545240-7349-42a3-8684-dd0664ba3890" xlink:to="loc_us-gaap_LicensingAgreementsMember_46bfc229-ea41-48c6-b907-e1aa9df65c85" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_4580a042-2edd-4606-9148-fefe3eb72774" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_1f545240-7349-42a3-8684-dd0664ba3890" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_4580a042-2edd-4606-9148-fefe3eb72774" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_61c52276-a902-4a8e-aa89-fc2536c8e1aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_fb349c82-636b-48c2-9265-3e0ba2047a62" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_61c52276-a902-4a8e-aa89-fc2536c8e1aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_61c52276-a902-4a8e-aa89-fc2536c8e1aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_61c52276-a902-4a8e-aa89-fc2536c8e1aa" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_61c52276-a902-4a8e-aa89-fc2536c8e1aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d830e876-c879-4d54-ac0a-075d0d653bb5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_61c52276-a902-4a8e-aa89-fc2536c8e1aa" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d830e876-c879-4d54-ac0a-075d0d653bb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_VaporsensIncMember_02319226-b5f9-4681-8120-b84ecb35d635" xlink:href="gntx-20230930.xsd#gntx_VaporsensIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d830e876-c879-4d54-ac0a-075d0d653bb5" xlink:to="loc_gntx_VaporsensIncMember_02319226-b5f9-4681-8120-b84ecb35d635" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ArgilIncMember_1c04a9cb-683b-42df-83b7-ffd67dbf43a9" xlink:href="gntx-20230930.xsd#gntx_ArgilIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d830e876-c879-4d54-ac0a-075d0d653bb5" xlink:to="loc_gntx_ArgilIncMember_1c04a9cb-683b-42df-83b7-ffd67dbf43a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AirCraftGlassMember_2fb515e0-76aa-4a37-93b3-1a101186b6a5" xlink:href="gntx-20230930.xsd#gntx_AirCraftGlassMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d830e876-c879-4d54-ac0a-075d0d653bb5" xlink:to="loc_gntx_AirCraftGlassMember_2fb515e0-76aa-4a37-93b3-1a101186b6a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_GuardianOpticalTechnologiesMember_0381ccbb-f65b-4b58-b818-d71759d53970" xlink:href="gntx-20230930.xsd#gntx_GuardianOpticalTechnologiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_d830e876-c879-4d54-ac0a-075d0d653bb5" xlink:to="loc_gntx_GuardianOpticalTechnologiesMember_0381ccbb-f65b-4b58-b818-d71759d53970" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/InvestmentsNarrativeDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#InvestmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/InvestmentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_407ac1f6-097d-48bd-8b10-e1a45af95288" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_d1f0fb6e-d569-4432-b99f-c6692a884ad5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_407ac1f6-097d-48bd-8b10-e1a45af95288" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_d1f0fb6e-d569-4432-b99f-c6692a884ad5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_094fb758-c25b-4d30-8843-fa1f067c97da" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_407ac1f6-097d-48bd-8b10-e1a45af95288" xlink:to="loc_us-gaap_EquitySecuritiesFvNiCurrentAndNoncurrent_094fb758-c25b-4d30-8843-fa1f067c97da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_5c45fa3a-2fbd-4abe-aa11-be36b8f3b88b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_407ac1f6-097d-48bd-8b10-e1a45af95288" xlink:to="loc_us-gaap_EquityMethodInvestments_5c45fa3a-2fbd-4abe-aa11-be36b8f3b88b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestments_dcb22492-8377-4071-8361-4d5676fb67f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_407ac1f6-097d-48bd-8b10-e1a45af95288" xlink:to="loc_us-gaap_ShortTermInvestments_dcb22492-8377-4071-8361-4d5676fb67f3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermInvestments_0ad83d6e-e074-4c40-a10d-b701afde8a24" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_407ac1f6-097d-48bd-8b10-e1a45af95288" xlink:to="loc_us-gaap_LongTermInvestments_0ad83d6e-e074-4c40-a10d-b701afde8a24" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8e3c1bad-b25a-48a4-8ac4-dcb6f4f76b5e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_407ac1f6-097d-48bd-8b10-e1a45af95288" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8e3c1bad-b25a-48a4-8ac4-dcb6f4f76b5e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_67b64a0d-ff69-4f76-9034-ed99de6f7193" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8e3c1bad-b25a-48a4-8ac4-dcb6f4f76b5e" xlink:to="loc_srt_RangeAxis_67b64a0d-ff69-4f76-9034-ed99de6f7193" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_67b64a0d-ff69-4f76-9034-ed99de6f7193_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_67b64a0d-ff69-4f76-9034-ed99de6f7193" xlink:to="loc_srt_RangeMember_67b64a0d-ff69-4f76-9034-ed99de6f7193_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4d4b429e-0c7b-42ad-9c59-670f7abf2cbc" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_67b64a0d-ff69-4f76-9034-ed99de6f7193" xlink:to="loc_srt_RangeMember_4d4b429e-0c7b-42ad-9c59-670f7abf2cbc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_ab1c6b8e-cc3d-4e67-9bd4-d0445426e31e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4d4b429e-0c7b-42ad-9c59-670f7abf2cbc" xlink:to="loc_srt_MinimumMember_ab1c6b8e-cc3d-4e67-9bd4-d0445426e31e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_f1971c36-cf2b-4059-8d07-9d3749590023" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_4d4b429e-0c7b-42ad-9c59-670f7abf2cbc" xlink:to="loc_srt_MaximumMember_f1971c36-cf2b-4059-8d07-9d3749590023" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_414caf83-b02a-406c-ad9d-bdcb2636c496" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8e3c1bad-b25a-48a4-8ac4-dcb6f4f76b5e" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_414caf83-b02a-406c-ad9d-bdcb2636c496" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_414caf83-b02a-406c-ad9d-bdcb2636c496_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_414caf83-b02a-406c-ad9d-bdcb2636c496" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_414caf83-b02a-406c-ad9d-bdcb2636c496_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_e8fb38e3-d3ac-4c88-9c0c-aadf44515e42" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_414caf83-b02a-406c-ad9d-bdcb2636c496" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_e8fb38e3-d3ac-4c88-9c0c-aadf44515e42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_GentexCorporationMember_a5d12d83-102c-4e4f-a1db-b9f8a200bfe8" xlink:href="gntx-20230930.xsd#gntx_GentexCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_e8fb38e3-d3ac-4c88-9c0c-aadf44515e42" xlink:to="loc_gntx_GentexCorporationMember_a5d12d83-102c-4e4f-a1db-b9f8a200bfe8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AdaskyLTDMember_7541e3fb-9418-47b9-80cc-b5123caaaaf4" xlink:href="gntx-20230930.xsd#gntx_AdaskyLTDMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_e8fb38e3-d3ac-4c88-9c0c-aadf44515e42" xlink:to="loc_gntx_AdaskyLTDMember_7541e3fb-9418-47b9-80cc-b5123caaaaf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_d9b38885-768f-48c6-a456-99aa64e6fae1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_8e3c1bad-b25a-48a4-8ac4-dcb6f4f76b5e" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_d9b38885-768f-48c6-a456-99aa64e6fae1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_d9b38885-768f-48c6-a456-99aa64e6fae1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_d9b38885-768f-48c6-a456-99aa64e6fae1" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_d9b38885-768f-48c6-a456-99aa64e6fae1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_b14fe94f-6735-4084-a2fb-886dcf2fd48e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_d9b38885-768f-48c6-a456-99aa64e6fae1" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_b14fe94f-6735-4084-a2fb-886dcf2fd48e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_LongTermInvestmentsMember_9949cfff-b454-48af-89d6-55d3e2a96356" xlink:href="gntx-20230930.xsd#gntx_LongTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_b14fe94f-6735-4084-a2fb-886dcf2fd48e" xlink:to="loc_gntx_LongTermInvestmentsMember_9949cfff-b454-48af-89d6-55d3e2a96356" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_9afff87a-6bf5-4ca3-8ecd-3e8a335f9784" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_b14fe94f-6735-4084-a2fb-886dcf2fd48e" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_9afff87a-6bf5-4ca3-8ecd-3e8a335f9784" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/InvestmentsScheduleofAssetsorLiabilitiesRecurringFairValueMeasurementsDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#InvestmentsScheduleofAssetsorLiabilitiesRecurringFairValueMeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/InvestmentsScheduleofAssetsorLiabilitiesRecurringFairValueMeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c5dcd452-3b6b-4b15-8af9-fdd4a849cc56" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_5a19c17c-5932-4602-ac87-28d40fea0c1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c5dcd452-3b6b-4b15-8af9-fdd4a849cc56" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_5a19c17c-5932-4602-ac87-28d40fea0c1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_RestrictedCashFairValueDisclosure_7ece9c89-e636-49a8-a467-d04b524c8634" xlink:href="gntx-20230930.xsd#gntx_RestrictedCashFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c5dcd452-3b6b-4b15-8af9-fdd4a849cc56" xlink:to="loc_gntx_RestrictedCashFairValueDisclosure_7ece9c89-e636-49a8-a467-d04b524c8634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_b46da418-07a1-4d13-989b-53fd88238e18" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c5dcd452-3b6b-4b15-8af9-fdd4a849cc56" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_b46da418-07a1-4d13-989b-53fd88238e18" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_ef073e78-3f4b-4a2a-997f-cd961f393b8c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c5dcd452-3b6b-4b15-8af9-fdd4a849cc56" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_ef073e78-3f4b-4a2a-997f-cd961f393b8c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a831a549-c135-4bd1-a756-5bd028168482" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_c5dcd452-3b6b-4b15-8af9-fdd4a849cc56" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a831a549-c135-4bd1-a756-5bd028168482" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeAxis_9dc497f6-8659-4c9f-a550-e1147b2772cc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a831a549-c135-4bd1-a756-5bd028168482" xlink:to="loc_us-gaap_InvestmentTypeAxis_9dc497f6-8659-4c9f-a550-e1147b2772cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_9dc497f6-8659-4c9f-a550-e1147b2772cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_9dc497f6-8659-4c9f-a550-e1147b2772cc" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_9dc497f6-8659-4c9f-a550-e1147b2772cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_ab6555f9-b2cb-4e6c-8f71-42ef29dd60f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentTypeCategorizationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_9dc497f6-8659-4c9f-a550-e1147b2772cc" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_ab6555f9-b2cb-4e6c-8f71-42ef29dd60f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_3669e99e-6e04-4e1d-9cd9-e6fcfea11ba5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_ab6555f9-b2cb-4e6c-8f71-42ef29dd60f3" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_3669e99e-6e04-4e1d-9cd9-e6fcfea11ba5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_bf5d39fc-1b5c-4075-895a-2f398d944954" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLongTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_ab6555f9-b2cb-4e6c-8f71-42ef29dd60f3" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_bf5d39fc-1b5c-4075-895a-2f398d944954" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_691c2076-9985-4a20-8e83-dfe43addef89" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a831a549-c135-4bd1-a756-5bd028168482" xlink:to="loc_us-gaap_FinancialInstrumentAxis_691c2076-9985-4a20-8e83-dfe43addef89" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_691c2076-9985-4a20-8e83-dfe43addef89_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_691c2076-9985-4a20-8e83-dfe43addef89" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_691c2076-9985-4a20-8e83-dfe43addef89_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_691c2076-9985-4a20-8e83-dfe43addef89" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_6f66b2d5-383c-4e6c-a83f-5f60c8b3e09a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_6f66b2d5-383c-4e6c-a83f-5f60c8b3e09a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CertificatesOfDepositMember_90614bdf-47ce-4c8e-9593-fb216a4363fd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CertificatesOfDepositMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:to="loc_us-gaap_CertificatesOfDepositMember_90614bdf-47ce-4c8e-9593-fb216a4363fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_e624dfbc-a676-4179-8c39-c7a6f7631c09" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_e624dfbc-a676-4179-8c39-c7a6f7631c09" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_7ac0de79-e21b-4b24-91c2-e5d61eae5ee2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_7ac0de79-e21b-4b24-91c2-e5d61eae5ee2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MunicipalBondsMember_3a74e7e6-18dd-4cf4-a00e-5b776b2ab1fe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MunicipalBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:to="loc_us-gaap_MunicipalBondsMember_3a74e7e6-18dd-4cf4-a00e-5b776b2ab1fe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDebtSecuritiesMember_ff65f38b-dae1-4c06-8715-69a3e36b4433" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:to="loc_us-gaap_OtherDebtSecuritiesMember_ff65f38b-dae1-4c06-8715-69a3e36b4433" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_150408a2-92b1-4e7e-a487-9b5a1619cb17" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_d1a82816-d0e3-4d9f-9327-23b7849525ff" xlink:to="loc_us-gaap_CommonStockMember_150408a2-92b1-4e7e-a487-9b5a1619cb17" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8964752f-3c0a-40f3-a5fc-403f8bf75259" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a831a549-c135-4bd1-a756-5bd028168482" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8964752f-3c0a-40f3-a5fc-403f8bf75259" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8964752f-3c0a-40f3-a5fc-403f8bf75259_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8964752f-3c0a-40f3-a5fc-403f8bf75259" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8964752f-3c0a-40f3-a5fc-403f8bf75259_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1ecb9615-0145-483d-a5d6-77de8d0d970f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_8964752f-3c0a-40f3-a5fc-403f8bf75259" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1ecb9615-0145-483d-a5d6-77de8d0d970f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_34e61e7f-7c80-4443-8fd9-6d28e9b49e61" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1ecb9615-0145-483d-a5d6-77de8d0d970f" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_34e61e7f-7c80-4443-8fd9-6d28e9b49e61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_e9157d95-8f6c-4b27-b250-354f3eb8320f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1ecb9615-0145-483d-a5d6-77de8d0d970f" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_e9157d95-8f6c-4b27-b250-354f3eb8320f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_9fc4ecdb-e821-470f-ab10-07d958e4c48f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1ecb9615-0145-483d-a5d6-77de8d0d970f" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_9fc4ecdb-e821-470f-ab10-07d958e4c48f" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/InvestmentsScheduleofAmortizedCostUnrealizedGainsandLossesandMarketValueofInvestmentSecuritiesDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#InvestmentsScheduleofAmortizedCostUnrealizedGainsandLossesandMarketValueofInvestmentSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/InvestmentsScheduleofAmortizedCostUnrealizedGainsandLossesandMarketValueofInvestmentSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_b2cec7cc-c2b4-4ad3-9421-cadd5421e14d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_2c98e756-db3f-423b-9c7c-14d735ed9110" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_b2cec7cc-c2b4-4ad3-9421-cadd5421e14d" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_2c98e756-db3f-423b-9c7c-14d735ed9110" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_821a71a3-b22f-46c0-8a53-3f2abb56f6b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_b2cec7cc-c2b4-4ad3-9421-cadd5421e14d" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_821a71a3-b22f-46c0-8a53-3f2abb56f6b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_a55b0d11-577b-438c-aa05-f058a9d7b3d5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_b2cec7cc-c2b4-4ad3-9421-cadd5421e14d" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_a55b0d11-577b-438c-aa05-f058a9d7b3d5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_5204b905-4cff-4cc3-925e-6bdde3c29a9f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_b2cec7cc-c2b4-4ad3-9421-cadd5421e14d" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_5204b905-4cff-4cc3-925e-6bdde3c29a9f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_c1459d60-8fdd-4fcc-8da7-cadeae706b7f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtSecuritiesAvailableForSaleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_b2cec7cc-c2b4-4ad3-9421-cadd5421e14d" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_c1459d60-8fdd-4fcc-8da7-cadeae706b7f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_InvestmentLengthAxis_8a5479c8-acb1-4eb5-883a-04c4a8f96974" xlink:href="gntx-20230930.xsd#gntx_InvestmentLengthAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_c1459d60-8fdd-4fcc-8da7-cadeae706b7f" xlink:to="loc_gntx_InvestmentLengthAxis_8a5479c8-acb1-4eb5-883a-04c4a8f96974" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_InvestmentLengthDomain_8a5479c8-acb1-4eb5-883a-04c4a8f96974_default" xlink:href="gntx-20230930.xsd#gntx_InvestmentLengthDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_gntx_InvestmentLengthAxis_8a5479c8-acb1-4eb5-883a-04c4a8f96974" xlink:to="loc_gntx_InvestmentLengthDomain_8a5479c8-acb1-4eb5-883a-04c4a8f96974_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_InvestmentLengthDomain_ae869380-b489-483c-94c7-3ef6039151c3" xlink:href="gntx-20230930.xsd#gntx_InvestmentLengthDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_gntx_InvestmentLengthAxis_8a5479c8-acb1-4eb5-883a-04c4a8f96974" xlink:to="loc_gntx_InvestmentLengthDomain_ae869380-b489-483c-94c7-3ef6039151c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_93be1913-215a-4369-9036-38f6cb4ae3e7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_InvestmentLengthDomain_ae869380-b489-483c-94c7-3ef6039151c3" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_93be1913-215a-4369-9036-38f6cb4ae3e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLongTermInvestmentsMember_3e18784a-6644-4722-949c-06aceb493c7f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLongTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_InvestmentLengthDomain_ae869380-b489-483c-94c7-3ef6039151c3" xlink:to="loc_us-gaap_OtherLongTermInvestmentsMember_3e18784a-6644-4722-949c-06aceb493c7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_3214a7d0-e58d-49ff-ad14-8266ec2fec0b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtSecuritiesAvailableForSaleTable_c1459d60-8fdd-4fcc-8da7-cadeae706b7f" xlink:to="loc_us-gaap_FinancialInstrumentAxis_3214a7d0-e58d-49ff-ad14-8266ec2fec0b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_3214a7d0-e58d-49ff-ad14-8266ec2fec0b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_3214a7d0-e58d-49ff-ad14-8266ec2fec0b" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_3214a7d0-e58d-49ff-ad14-8266ec2fec0b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_3214a7d0-e58d-49ff-ad14-8266ec2fec0b" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetBackedSecuritiesMember_4b3d0484-bbf6-424d-8767-04e2d776b628" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetBackedSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:to="loc_us-gaap_AssetBackedSecuritiesMember_4b3d0484-bbf6-424d-8767-04e2d776b628" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CertificatesOfDepositMember_819ce5ff-e676-4240-9baa-bf8d71b478b0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CertificatesOfDepositMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:to="loc_us-gaap_CertificatesOfDepositMember_819ce5ff-e676-4240-9baa-bf8d71b478b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_c2245fe2-6c31-4d05-addd-8af49c9fa9a8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_c2245fe2-6c31-4d05-addd-8af49c9fa9a8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_144fc916-5871-4cd0-a45b-da787db1373d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_144fc916-5871-4cd0-a45b-da787db1373d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MunicipalBondsMember_4082ac53-d845-40e3-871f-63c9ff564b7c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MunicipalBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:to="loc_us-gaap_MunicipalBondsMember_4082ac53-d845-40e3-871f-63c9ff564b7c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherDebtSecuritiesMember_fa563f3b-b217-4155-9317-111494617921" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:to="loc_us-gaap_OtherDebtSecuritiesMember_fa563f3b-b217-4155-9317-111494617921" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_c180fbd1-856a-4ba1-8580-7e252d2a7f7a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1aa7b185-0771-4562-9e66-4d90f26f01a4" xlink:to="loc_us-gaap_CommonStockMember_c180fbd1-856a-4ba1-8580-7e252d2a7f7a" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/InvestmentsScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#InvestmentsScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/InvestmentsScheduleofInvestmentsClassifiedbyContractualMaturityDateDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0fcaccbe-6cce-4816-8452-f6cca038ba44" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_ed46881e-7374-457d-974d-27a7c5d4bd20" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0fcaccbe-6cce-4816-8452-f6cca038ba44" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue_ed46881e-7374-457d-974d-27a7c5d4bd20" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_602ca3a8-5022-4e12-a47a-cf20341211e0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0fcaccbe-6cce-4816-8452-f6cca038ba44" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue_602ca3a8-5022-4e12-a47a-cf20341211e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_DebtSecuritiesAvailableForSaleMaturityAllocatedAndSingleMaturityDateAfterFiveYearsFairValue_9e29be2f-dce5-433d-9aa0-000ba765b7bc" xlink:href="gntx-20230930.xsd#gntx_DebtSecuritiesAvailableForSaleMaturityAllocatedAndSingleMaturityDateAfterFiveYearsFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0fcaccbe-6cce-4816-8452-f6cca038ba44" xlink:to="loc_gntx_DebtSecuritiesAvailableForSaleMaturityAllocatedAndSingleMaturityDateAfterFiveYearsFairValue_9e29be2f-dce5-433d-9aa0-000ba765b7bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_4c1abfec-0a7d-49ab-b6c8-d142f2bc6761" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0fcaccbe-6cce-4816-8452-f6cca038ba44" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_4c1abfec-0a7d-49ab-b6c8-d142f2bc6761" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_FinancialInstrumentsTable_ab4db762-06a9-480c-9ef9-fae4f8a8c323" xlink:href="gntx-20230930.xsd#gntx_FinancialInstrumentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_0fcaccbe-6cce-4816-8452-f6cca038ba44" xlink:to="loc_gntx_FinancialInstrumentsTable_ab4db762-06a9-480c-9ef9-fae4f8a8c323" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_755e641d-3181-4c66-9fa8-31f5e983a994" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_gntx_FinancialInstrumentsTable_ab4db762-06a9-480c-9ef9-fae4f8a8c323" xlink:to="loc_us-gaap_FinancialInstrumentAxis_755e641d-3181-4c66-9fa8-31f5e983a994" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_755e641d-3181-4c66-9fa8-31f5e983a994_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_755e641d-3181-4c66-9fa8-31f5e983a994" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_755e641d-3181-4c66-9fa8-31f5e983a994_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_5a8f8d95-e1d9-4f9b-a8ac-8a4f9ea9fa66" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_755e641d-3181-4c66-9fa8-31f5e983a994" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_5a8f8d95-e1d9-4f9b-a8ac-8a4f9ea9fa66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedIncomeSecuritiesMember_e07739cb-2be3-4a6a-beb6-92de9e45686c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FixedIncomeSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_5a8f8d95-e1d9-4f9b-a8ac-8a4f9ea9fa66" xlink:to="loc_us-gaap_FixedIncomeSecuritiesMember_e07739cb-2be3-4a6a-beb6-92de9e45686c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/StockBasedCompensationPlansNarrativeDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#StockBasedCompensationPlansNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/StockBasedCompensationPlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPlans_f6247f3b-28fb-4dab-9a12-c7973a6f0350" xlink:href="gntx-20230930.xsd#gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPlans_f6247f3b-28fb-4dab-9a12-c7973a6f0350" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_5f4b6c1e-1e5e-4506-adcd-822055d60d61" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_5f4b6c1e-1e5e-4506-adcd-822055d60d61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod_0a8d0320-018c-4d61-896b-c9d0c65a6b7a" xlink:href="gntx-20230930.xsd#gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod_0a8d0320-018c-4d61-896b-c9d0c65a6b7a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_b3d5d638-562d-4a7c-9975-c1d32cf0b2d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_b3d5d638-562d-4a7c-9975-c1d32cf0b2d0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_c237214f-aab9-4c18-9857-3e6637737354" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_c237214f-aab9-4c18-9857-3e6637737354" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_9772b915-df65-4d58-a668-57a6b89d8831" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_9772b915-df65-4d58-a668-57a6b89d8831" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_3720defc-89ef-4c33-9fcf-344aa0b7da85" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_3720defc-89ef-4c33-9fcf-344aa0b7da85" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_874d6555-5e9f-424a-b35a-cb1c36cced69" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_874d6555-5e9f-424a-b35a-cb1c36cced69" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationRestrictedPeriod_1e4f8a18-3a91-4890-a099-672dab16f9d2" xlink:href="gntx-20230930.xsd#gntx_ShareBasedCompensationRestrictedPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_gntx_ShareBasedCompensationRestrictedPeriod_1e4f8a18-3a91-4890-a099-672dab16f9d2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockExpense_52bee72b-1674-4066-b464-356d03c705c3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_RestrictedStockExpense_52bee72b-1674-4066-b464-356d03c705c3" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate_1d9b991d-4bda-42ba-a3b0-f3cc378b0227" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountFromMarketPricePurchaseDate_1d9b991d-4bda-42ba-a3b0-f3cc378b0227" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountRecognizedAsCompensationExpense_e3f146ec-9028-48cb-b033-51e7074cae64" xlink:href="gntx-20230930.xsd#gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountRecognizedAsCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardDiscountRecognizedAsCompensationExpense_e3f146ec-9028-48cb-b033-51e7074cae64" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e9eb55be-00b0-4cca-9456-85b08c2cdad2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2e7b7977-43d1-4d34-a580-72bd725e4bda" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e9eb55be-00b0-4cca-9456-85b08c2cdad2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_1a94c497-2c47-43f1-b42c-11ba29dcebdd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e9eb55be-00b0-4cca-9456-85b08c2cdad2" xlink:to="loc_us-gaap_PlanNameAxis_1a94c497-2c47-43f1-b42c-11ba29dcebdd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_1a94c497-2c47-43f1-b42c-11ba29dcebdd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_1a94c497-2c47-43f1-b42c-11ba29dcebdd" xlink:to="loc_us-gaap_PlanNameDomain_1a94c497-2c47-43f1-b42c-11ba29dcebdd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_2be3f842-6fab-4f9f-af63-27c7d65a415b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_1a94c497-2c47-43f1-b42c-11ba29dcebdd" xlink:to="loc_us-gaap_PlanNameDomain_2be3f842-6fab-4f9f-af63-27c7d65a415b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OmnibusIncentivePlanMember_6a49e183-a835-4378-906c-32b5c6b4594f" xlink:href="gntx-20230930.xsd#gntx_OmnibusIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_2be3f842-6fab-4f9f-af63-27c7d65a415b" xlink:to="loc_gntx_OmnibusIncentivePlanMember_6a49e183-a835-4378-906c-32b5c6b4594f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_EmployeeStockOptionPlanMember_eefb8c81-69f0-43c8-8287-d547e889aba8" xlink:href="gntx-20230930.xsd#gntx_EmployeeStockOptionPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_2be3f842-6fab-4f9f-af63-27c7d65a415b" xlink:to="loc_gntx_EmployeeStockOptionPlanMember_eefb8c81-69f0-43c8-8287-d547e889aba8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_RestrictedStockPlanMember_6787498f-41d5-47be-b7f0-f8ddda9e809f" xlink:href="gntx-20230930.xsd#gntx_RestrictedStockPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_2be3f842-6fab-4f9f-af63-27c7d65a415b" xlink:to="loc_gntx_RestrictedStockPlanMember_6787498f-41d5-47be-b7f0-f8ddda9e809f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_GentexCorporationEmployeeStockPurchasePlanMember_8dc97dbd-a04a-4bad-8a7b-a3eda5fc927b" xlink:href="gntx-20230930.xsd#gntx_GentexCorporationEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_2be3f842-6fab-4f9f-af63-27c7d65a415b" xlink:to="loc_gntx_GentexCorporationEmployeeStockPurchasePlanMember_8dc97dbd-a04a-4bad-8a7b-a3eda5fc927b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_2b266530-65b4-44e1-9416-a6a0683dba22" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e9eb55be-00b0-4cca-9456-85b08c2cdad2" xlink:to="loc_srt_RangeAxis_2b266530-65b4-44e1-9416-a6a0683dba22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_2b266530-65b4-44e1-9416-a6a0683dba22_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_2b266530-65b4-44e1-9416-a6a0683dba22" xlink:to="loc_srt_RangeMember_2b266530-65b4-44e1-9416-a6a0683dba22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_b87288c8-f5a7-46ad-961f-3041a07c1daf" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_2b266530-65b4-44e1-9416-a6a0683dba22" xlink:to="loc_srt_RangeMember_b87288c8-f5a7-46ad-961f-3041a07c1daf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_608cfd4e-8095-4a0c-bfbd-098f2bf651b2" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b87288c8-f5a7-46ad-961f-3041a07c1daf" xlink:to="loc_srt_MinimumMember_608cfd4e-8095-4a0c-bfbd-098f2bf651b2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_ebd5f7b2-2819-4cb8-92ec-48236184646c" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_b87288c8-f5a7-46ad-961f-3041a07c1daf" xlink:to="loc_srt_MaximumMember_ebd5f7b2-2819-4cb8-92ec-48236184646c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f9e213f6-24e6-48cd-875c-dbbb4883ff5d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e9eb55be-00b0-4cca-9456-85b08c2cdad2" xlink:to="loc_us-gaap_AwardTypeAxis_f9e213f6-24e6-48cd-875c-dbbb4883ff5d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f9e213f6-24e6-48cd-875c-dbbb4883ff5d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f9e213f6-24e6-48cd-875c-dbbb4883ff5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f9e213f6-24e6-48cd-875c-dbbb4883ff5d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_73730bdd-8295-4aab-9c50-25da108d98ab" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f9e213f6-24e6-48cd-875c-dbbb4883ff5d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_73730bdd-8295-4aab-9c50-25da108d98ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockCompensationPlanMember_021ef6cc-86a8-4542-8626-0799fe3909a3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockCompensationPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_73730bdd-8295-4aab-9c50-25da108d98ab" xlink:to="loc_us-gaap_StockCompensationPlanMember_021ef6cc-86a8-4542-8626-0799fe3909a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_6ec4e764-6b35-4bf7-a2a8-27aee397d0d3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_73730bdd-8295-4aab-9c50-25da108d98ab" xlink:to="loc_us-gaap_PerformanceSharesMember_6ec4e764-6b35-4bf7-a2a8-27aee397d0d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_PerformanceShareAwardsMember_dfe3f9ea-3d35-4556-b902-0e61c23bef6f" xlink:href="gntx-20230930.xsd#gntx_PerformanceShareAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_73730bdd-8295-4aab-9c50-25da108d98ab" xlink:to="loc_gntx_PerformanceShareAwardsMember_dfe3f9ea-3d35-4556-b902-0e61c23bef6f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_c7d91575-270c-4119-ad8c-ea4452f32365" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_e9eb55be-00b0-4cca-9456-85b08c2cdad2" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_c7d91575-270c-4119-ad8c-ea4452f32365" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c7d91575-270c-4119-ad8c-ea4452f32365_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_c7d91575-270c-4119-ad8c-ea4452f32365" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_c7d91575-270c-4119-ad8c-ea4452f32365_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_07554e3b-cea9-41f0-9cb8-61e646abf3a3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_c7d91575-270c-4119-ad8c-ea4452f32365" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_07554e3b-cea9-41f0-9cb8-61e646abf3a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_3fd5e715-6cfe-4cc7-a0e4-d344e41845dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_07554e3b-cea9-41f0-9cb8-61e646abf3a3" xlink:to="loc_us-gaap_EmployeeStockMember_3fd5e715-6cfe-4cc7-a0e4-d344e41845dc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/StockBasedCompensationPlansScheduleofSharesIssuedNetofSharesCanceledExpiredDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#StockBasedCompensationPlansScheduleofSharesIssuedNetofSharesCanceledExpiredDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/StockBasedCompensationPlansScheduleofSharesIssuedNetofSharesCanceledExpiredDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_10fc25f8-e02a-4677-9b61-5b2efcb3006b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_e7c072ee-aba4-4762-9ec6-3c418a634a7d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_10fc25f8-e02a-4677-9b61-5b2efcb3006b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_e7c072ee-aba4-4762-9ec6-3c418a634a7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_76ce8d90-dc0f-4255-9b5d-96781e7c7029" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_10fc25f8-e02a-4677-9b61-5b2efcb3006b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_76ce8d90-dc0f-4255-9b5d-96781e7c7029" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod_6e37b492-33ac-485a-b616-d8399844cc11" xlink:href="gntx-20230930.xsd#gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_10fc25f8-e02a-4677-9b61-5b2efcb3006b" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedAwardGrantedInPeriod_6e37b492-33ac-485a-b616-d8399844cc11" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConversionRate_86452c7c-cc37-4ab0-9693-944c51fba6a6" xlink:href="gntx-20230930.xsd#gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_10fc25f8-e02a-4677-9b61-5b2efcb3006b" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsConversionRate_86452c7c-cc37-4ab0-9693-944c51fba6a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentConversionRate_e37f0f61-8693-4ee4-968e-5619fc21ac40" xlink:href="gntx-20230930.xsd#gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentConversionRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_10fc25f8-e02a-4677-9b61-5b2efcb3006b" xlink:to="loc_gntx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentConversionRate_e37f0f61-8693-4ee4-968e-5619fc21ac40" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_b251f679-9f7e-4d91-b8a9-7e20293d1ea7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_10fc25f8-e02a-4677-9b61-5b2efcb3006b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_b251f679-9f7e-4d91-b8a9-7e20293d1ea7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1c97d008-aece-4757-998b-617f37b4e0af" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_10fc25f8-e02a-4677-9b61-5b2efcb3006b" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1c97d008-aece-4757-998b-617f37b4e0af" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e0e6f571-3d10-4627-88c0-4cc8ff9d8422" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1c97d008-aece-4757-998b-617f37b4e0af" xlink:to="loc_us-gaap_AwardTypeAxis_e0e6f571-3d10-4627-88c0-4cc8ff9d8422" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e0e6f571-3d10-4627-88c0-4cc8ff9d8422_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e0e6f571-3d10-4627-88c0-4cc8ff9d8422" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e0e6f571-3d10-4627-88c0-4cc8ff9d8422_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01e02dbc-587f-4865-a987-e25ef18d8ad0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e0e6f571-3d10-4627-88c0-4cc8ff9d8422" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01e02dbc-587f-4865-a987-e25ef18d8ad0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_NonQualifiedStockOptionMember_002af975-3f38-4a5d-aa18-23ded6fd894a" xlink:href="gntx-20230930.xsd#gntx_NonQualifiedStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01e02dbc-587f-4865-a987-e25ef18d8ad0" xlink:to="loc_gntx_NonQualifiedStockOptionMember_002af975-3f38-4a5d-aa18-23ded6fd894a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_b4775e67-1135-4348-a2a6-86760b4b4616" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01e02dbc-587f-4865-a987-e25ef18d8ad0" xlink:to="loc_us-gaap_RestrictedStockMember_b4775e67-1135-4348-a2a6-86760b4b4616" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_3f7c6a00-5349-4b67-9ca4-3f5d3b3cb66e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_01e02dbc-587f-4865-a987-e25ef18d8ad0" xlink:to="loc_us-gaap_PerformanceSharesMember_3f7c6a00-5349-4b67-9ca4-3f5d3b3cb66e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_6ede8ec5-664b-432a-8744-359c9b5b838d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1c97d008-aece-4757-998b-617f37b4e0af" xlink:to="loc_us-gaap_PlanNameAxis_6ede8ec5-664b-432a-8744-359c9b5b838d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_6ede8ec5-664b-432a-8744-359c9b5b838d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_6ede8ec5-664b-432a-8744-359c9b5b838d" xlink:to="loc_us-gaap_PlanNameDomain_6ede8ec5-664b-432a-8744-359c9b5b838d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_22866841-658e-4d48-a917-e5528fe87de9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_6ede8ec5-664b-432a-8744-359c9b5b838d" xlink:to="loc_us-gaap_PlanNameDomain_22866841-658e-4d48-a917-e5528fe87de9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OmnibusIncentivePlanMember_fca24e27-24a1-49e6-8369-318d89c0e316" xlink:href="gntx-20230930.xsd#gntx_OmnibusIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_22866841-658e-4d48-a917-e5528fe87de9" xlink:to="loc_gntx_OmnibusIncentivePlanMember_fca24e27-24a1-49e6-8369-318d89c0e316" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/ComprehensiveIncomeLossScheduleofAOCIRollforwardDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#ComprehensiveIncomeLossScheduleofAOCIRollforwardDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/ComprehensiveIncomeLossScheduleofAOCIRollforwardDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bc3401c-01ed-4299-9d06-0b9f367f97a8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_eeba38b7-7ec2-42c0-9124-16a0c709a155" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bc3401c-01ed-4299-9d06-0b9f367f97a8" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_eeba38b7-7ec2-42c0-9124-16a0c709a155" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_5dc152e2-e1e1-485a-a3bc-6eb9642fce22" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_eeba38b7-7ec2-42c0-9124-16a0c709a155" xlink:to="loc_us-gaap_StockholdersEquity_5dc152e2-e1e1-485a-a3bc-6eb9642fce22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_9742d0f8-cacb-4ef4-96d2-1950fb1bc316" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_eeba38b7-7ec2-42c0-9124-16a0c709a155" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_9742d0f8-cacb-4ef4-96d2-1950fb1bc316" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_b4e7ac13-def2-44ee-bd73-4568d8c24387" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_eeba38b7-7ec2-42c0-9124-16a0c709a155" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_b4e7ac13-def2-44ee-bd73-4568d8c24387" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_37297f7a-3899-4edd-b56c-23fe8eaba6ff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_eeba38b7-7ec2-42c0-9124-16a0c709a155" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_37297f7a-3899-4edd-b56c-23fe8eaba6ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_5daec240-c77c-4982-8798-0abffa2af07e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_5feb07a5-005c-463f-bf37-2183db5204dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_2bc3401c-01ed-4299-9d06-0b9f367f97a8" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_5feb07a5-005c-463f-bf37-2183db5204dc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_e37d1516-782b-4545-b23a-783b53b5450d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_5feb07a5-005c-463f-bf37-2183db5204dc" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_e37d1516-782b-4545-b23a-783b53b5450d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_e37d1516-782b-4545-b23a-783b53b5450d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_e37d1516-782b-4545-b23a-783b53b5450d" xlink:to="loc_us-gaap_EquityComponentDomain_e37d1516-782b-4545-b23a-783b53b5450d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_37094ddb-c62f-4636-9849-3067566f9add" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_e37d1516-782b-4545-b23a-783b53b5450d" xlink:to="loc_us-gaap_EquityComponentDomain_37094ddb-c62f-4636-9849-3067566f9add" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1d29f7fc-b0ab-447e-b425-e163d577f288" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_37094ddb-c62f-4636-9849-3067566f9add" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1d29f7fc-b0ab-447e-b425-e163d577f288" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_29a6f3a7-4789-4d18-bf11-d0444bf95b5c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1d29f7fc-b0ab-447e-b425-e163d577f288" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_29a6f3a7-4789-4d18-bf11-d0444bf95b5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_0a10b98d-9f6c-4fa0-95a8-ad7362b23fee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1d29f7fc-b0ab-447e-b425-e163d577f288" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_0a10b98d-9f6c-4fa0-95a8-ad7362b23fee" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/ComprehensiveIncomeLossScheduleofReclassificationsOutofAccumulatedOtherComprehensiveLossDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#ComprehensiveIncomeLossScheduleofReclassificationsOutofAccumulatedOtherComprehensiveLossDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/ComprehensiveIncomeLossScheduleofReclassificationsOutofAccumulatedOtherComprehensiveLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_77256707-a5d3-4b08-872c-cfcb64783f08" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesFvNiRealizedGainLoss_700c1be1-1eab-4a61-b6c4-3f4dbe987078" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquitySecuritiesFvNiRealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_77256707-a5d3-4b08-872c-cfcb64783f08" xlink:to="loc_us-gaap_EquitySecuritiesFvNiRealizedGainLoss_700c1be1-1eab-4a61-b6c4-3f4dbe987078" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_1c333538-978e-4044-ab2e-921010b8b08e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_77256707-a5d3-4b08-872c-cfcb64783f08" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_1c333538-978e-4044-ab2e-921010b8b08e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_dc5bf86f-9e88-4cfb-8133-6b00a63fafa3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_77256707-a5d3-4b08-872c-cfcb64783f08" xlink:to="loc_us-gaap_NetIncomeLoss_dc5bf86f-9e88-4cfb-8133-6b00a63fafa3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_7e96e119-cb62-4e10-939e-9dbe287c086d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ReclassificationAdjustmentOutOfAccumulatedOtherComprehensiveIncomeLineItems_77256707-a5d3-4b08-872c-cfcb64783f08" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_7e96e119-cb62-4e10-939e-9dbe287c086d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_7b99aefa-7b96-4416-808f-66ec677200bd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_7e96e119-cb62-4e10-939e-9dbe287c086d" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_7b99aefa-7b96-4416-808f-66ec677200bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_7b99aefa-7b96-4416-808f-66ec677200bd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_7b99aefa-7b96-4416-808f-66ec677200bd" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_7b99aefa-7b96-4416-808f-66ec677200bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_ab09b059-96a0-44e4-8d3f-a1f080f17963" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeAxis_7b99aefa-7b96-4416-808f-66ec677200bd" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_ab09b059-96a0-44e4-8d3f-a1f080f17963" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_c8a0b424-9199-4525-994e-e1976ff3faa6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeDomain_ab09b059-96a0-44e4-8d3f-a1f080f17963" xlink:to="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeMember_c8a0b424-9199-4525-994e-e1976ff3faa6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_80f8192f-a6df-428b-9ece-2367f6a6ce38" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReclassificationOutOfAccumulatedOtherComprehensiveIncomeTable_7e96e119-cb62-4e10-939e-9dbe287c086d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_80f8192f-a6df-428b-9ece-2367f6a6ce38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_80f8192f-a6df-428b-9ece-2367f6a6ce38_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_80f8192f-a6df-428b-9ece-2367f6a6ce38" xlink:to="loc_us-gaap_EquityComponentDomain_80f8192f-a6df-428b-9ece-2367f6a6ce38_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_04c826f1-5c0b-401a-9d82-bf4e306e9ff8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_80f8192f-a6df-428b-9ece-2367f6a6ce38" xlink:to="loc_us-gaap_EquityComponentDomain_04c826f1-5c0b-401a-9d82-bf4e306e9ff8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_40ffddfd-a110-4f84-8986-3f7e8123f3b0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_04c826f1-5c0b-401a-9d82-bf4e306e9ff8" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_40ffddfd-a110-4f84-8986-3f7e8123f3b0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/DebtandFinancingArrangementsDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#DebtandFinancingArrangementsDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/DebtandFinancingArrangementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_a0f1628f-f9d6-49b1-8990-0db37d412447" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_d0536982-ab2e-4136-9937-6fd0fe6c3163" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a0f1628f-f9d6-49b1-8990-0db37d412447" xlink:to="loc_us-gaap_DebtInstrumentTerm_d0536982-ab2e-4136-9937-6fd0fe6c3163" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_a9ed6627-8b4f-4b8a-8fde-af355800e2cb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a0f1628f-f9d6-49b1-8990-0db37d412447" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_a9ed6627-8b4f-4b8a-8fde-af355800e2cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_DebtInstrumentAdditionalBorrowingsAvailableFaceAmount_6d410bbb-5ce7-4ebb-8954-84d3cc0283e6" xlink:href="gntx-20230930.xsd#gntx_DebtInstrumentAdditionalBorrowingsAvailableFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a0f1628f-f9d6-49b1-8990-0db37d412447" xlink:to="loc_gntx_DebtInstrumentAdditionalBorrowingsAvailableFaceAmount_6d410bbb-5ce7-4ebb-8954-84d3cc0283e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_c21021fb-8798-4f10-93bd-8664669d2e19" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a0f1628f-f9d6-49b1-8990-0db37d412447" xlink:to="loc_us-gaap_LongTermDebt_c21021fb-8798-4f10-93bd-8664669d2e19" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_f0c6acdb-de09-4ff1-9206-539220da50b9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a0f1628f-f9d6-49b1-8990-0db37d412447" xlink:to="loc_us-gaap_DebtInstrumentTable_f0c6acdb-de09-4ff1-9206-539220da50b9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_4f1fed82-23c8-40eb-88de-e044372a05af" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_f0c6acdb-de09-4ff1-9206-539220da50b9" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_4f1fed82-23c8-40eb-88de-e044372a05af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_4f1fed82-23c8-40eb-88de-e044372a05af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4f1fed82-23c8-40eb-88de-e044372a05af" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_4f1fed82-23c8-40eb-88de-e044372a05af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_060b49ed-8eee-408d-85da-4c319a0b0ed4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_4f1fed82-23c8-40eb-88de-e044372a05af" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_060b49ed-8eee-408d-85da-4c319a0b0ed4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_60f006e3-ce69-4791-bf1d-1a3ba1983f37" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_060b49ed-8eee-408d-85da-4c319a0b0ed4" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_60f006e3-ce69-4791-bf1d-1a3ba1983f37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_5a99425d-3114-48db-a310-046e42488398" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_060b49ed-8eee-408d-85da-4c319a0b0ed4" xlink:to="loc_us-gaap_LetterOfCreditMember_5a99425d-3114-48db-a310-046e42488398" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_SwingLoansMember_a3d97072-f8d4-4189-8c3a-5549594e993b" xlink:href="gntx-20230930.xsd#gntx_SwingLoansMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_060b49ed-8eee-408d-85da-4c319a0b0ed4" xlink:to="loc_gntx_SwingLoansMember_a3d97072-f8d4-4189-8c3a-5549594e993b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/SegmentReportingNarrativeDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#SegmentReportingNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/SegmentReportingNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_fb051d93-df05-4425-a80e-3fc1d8a5dc72" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_348da8f6-abb7-4001-980b-9eec5090f731" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_fb051d93-df05-4425-a80e-3fc1d8a5dc72" xlink:to="loc_us-gaap_NumberOfReportableSegments_348da8f6-abb7-4001-980b-9eec5090f731" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_73d87338-c656-444c-af2e-8fa75373bb51" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_fb051d93-df05-4425-a80e-3fc1d8a5dc72" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_73d87338-c656-444c-af2e-8fa75373bb51" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_ad32a954-f238-48ce-b458-735e530c621f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_73d87338-c656-444c-af2e-8fa75373bb51" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_ad32a954-f238-48ce-b458-735e530c621f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_ad32a954-f238-48ce-b458-735e530c621f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ad32a954-f238-48ce-b458-735e530c621f" xlink:to="loc_us-gaap_SegmentDomain_ad32a954-f238-48ce-b458-735e530c621f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_fe90dc16-8efa-463d-bea8-c9dd1b838a76" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ad32a954-f238-48ce-b458-735e530c621f" xlink:to="loc_us-gaap_SegmentDomain_fe90dc16-8efa-463d-bea8-c9dd1b838a76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherSegmentsMember_a71ee315-352e-4165-bddf-7e0487aff3ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllOtherSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_fe90dc16-8efa-463d-bea8-c9dd1b838a76" xlink:to="loc_us-gaap_AllOtherSegmentsMember_a71ee315-352e-4165-bddf-7e0487aff3ba" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/SegmentReportingScheduleofSegmentReportingDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#SegmentReportingScheduleofSegmentReportingDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/SegmentReportingScheduleofSegmentReportingDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_7da8861b-2ee1-4f63-af26-32f8668c6fcd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_096adefd-819d-4013-9514-2c3f1eeeac0b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_7da8861b-2ee1-4f63-af26-32f8668c6fcd" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_096adefd-819d-4013-9514-2c3f1eeeac0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_3fea5f86-72ad-41ad-8b0c-a2b036372a68" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_7da8861b-2ee1-4f63-af26-32f8668c6fcd" xlink:to="loc_us-gaap_OperatingIncomeLoss_3fea5f86-72ad-41ad-8b0c-a2b036372a68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_a9725788-eac0-443b-b0fa-d5fefe6f0ca8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_7da8861b-2ee1-4f63-af26-32f8668c6fcd" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_a9725788-eac0-443b-b0fa-d5fefe6f0ca8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_ab39d219-fdb0-4a4d-88a6-1ecaa5087348" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_a9725788-eac0-443b-b0fa-d5fefe6f0ca8" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_ab39d219-fdb0-4a4d-88a6-1ecaa5087348" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_ab39d219-fdb0-4a4d-88a6-1ecaa5087348_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ab39d219-fdb0-4a4d-88a6-1ecaa5087348" xlink:to="loc_us-gaap_SegmentDomain_ab39d219-fdb0-4a4d-88a6-1ecaa5087348_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_bfa6656e-1e9a-499b-827a-11cf15083356" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_ab39d219-fdb0-4a4d-88a6-1ecaa5087348" xlink:to="loc_us-gaap_SegmentDomain_bfa6656e-1e9a-499b-827a-11cf15083356" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AutomotiveProductsSegmentMember_96498eb9-6d1e-456b-885c-d65ffa1a7d96" xlink:href="gntx-20230930.xsd#gntx_AutomotiveProductsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_bfa6656e-1e9a-499b-827a-11cf15083356" xlink:to="loc_gntx_AutomotiveProductsSegmentMember_96498eb9-6d1e-456b-885c-d65ffa1a7d96" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllOtherSegmentsMember_c3b90d9d-e1d6-49f8-90c3-3a45f6caa4b8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllOtherSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_bfa6656e-1e9a-499b-827a-11cf15083356" xlink:to="loc_us-gaap_AllOtherSegmentsMember_c3b90d9d-e1d6-49f8-90c3-3a45f6caa4b8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/RevenueDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#RevenueDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/RevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_9320ce99-ac78-4225-84f9-7560f65cb42d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_2bf95245-7d0b-4960-9e46-6b8d2c265c21" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_9320ce99-ac78-4225-84f9-7560f65cb42d" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_2bf95245-7d0b-4960-9e46-6b8d2c265c21" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_2a8b5fe3-e05d-4a97-bd3b-4d9856ef63b6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_9320ce99-ac78-4225-84f9-7560f65cb42d" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_2a8b5fe3-e05d-4a97-bd3b-4d9856ef63b6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_ab4b9b7a-4382-4489-b2cf-1b5eb0d30a8b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_2a8b5fe3-e05d-4a97-bd3b-4d9856ef63b6" xlink:to="loc_srt_StatementGeographicalAxis_ab4b9b7a-4382-4489-b2cf-1b5eb0d30a8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_ab4b9b7a-4382-4489-b2cf-1b5eb0d30a8b_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_ab4b9b7a-4382-4489-b2cf-1b5eb0d30a8b" xlink:to="loc_srt_SegmentGeographicalDomain_ab4b9b7a-4382-4489-b2cf-1b5eb0d30a8b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_21deb743-6046-4c13-befb-3861a0011c9c" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_ab4b9b7a-4382-4489-b2cf-1b5eb0d30a8b" xlink:to="loc_srt_SegmentGeographicalDomain_21deb743-6046-4c13-befb-3861a0011c9c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_d354965e-e3b0-4efd-a7aa-9a07438dc630" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_21deb743-6046-4c13-befb-3861a0011c9c" xlink:to="loc_country_US_d354965e-e3b0-4efd-a7aa-9a07438dc630" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_2a478eb8-0305-4da0-999b-00121779438b" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_21deb743-6046-4c13-befb-3861a0011c9c" xlink:to="loc_country_DE_2a478eb8-0305-4da0-999b-00121779438b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_JP_740a8d7b-ee59-4120-b8de-aed11fcc7ed5" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_JP"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_21deb743-6046-4c13-befb-3861a0011c9c" xlink:to="loc_country_JP_740a8d7b-ee59-4120-b8de-aed11fcc7ed5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_MX_379b0064-80fc-4844-aa35-809e8ccb0074" xlink:href="https://xbrl.sec.gov/country/2023/country-2023.xsd#country_MX"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_21deb743-6046-4c13-befb-3861a0011c9c" xlink:to="loc_country_MX_379b0064-80fc-4844-aa35-809e8ccb0074" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OtherCountriesMember_3378016d-74be-431c-957f-9f5c749ab0ee" xlink:href="gntx-20230930.xsd#gntx_OtherCountriesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_21deb743-6046-4c13-befb-3861a0011c9c" xlink:to="loc_gntx_OtherCountriesMember_3378016d-74be-431c-957f-9f5c749ab0ee" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_f368f199-f85a-4c01-952d-c703a29f8b43" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_2a8b5fe3-e05d-4a97-bd3b-4d9856ef63b6" xlink:to="loc_srt_ProductOrServiceAxis_f368f199-f85a-4c01-952d-c703a29f8b43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_f368f199-f85a-4c01-952d-c703a29f8b43_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_f368f199-f85a-4c01-952d-c703a29f8b43" xlink:to="loc_srt_ProductsAndServicesDomain_f368f199-f85a-4c01-952d-c703a29f8b43_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_99f3f241-d6bf-48bc-9045-04a0b2ab5bc9" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_f368f199-f85a-4c01-952d-c703a29f8b43" xlink:to="loc_srt_ProductsAndServicesDomain_99f3f241-d6bf-48bc-9045-04a0b2ab5bc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AutomotiveProductsMember_a1fc71ad-2d73-4eb0-9294-9c4d1f4288c6" xlink:href="gntx-20230930.xsd#gntx_AutomotiveProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_99f3f241-d6bf-48bc-9045-04a0b2ab5bc9" xlink:to="loc_gntx_AutomotiveProductsMember_a1fc71ad-2d73-4eb0-9294-9c4d1f4288c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AutomotiveMirrorsElectronicsMember_901c0bde-53ee-46a3-bd4b-1c8bb69f0790" xlink:href="gntx-20230930.xsd#gntx_AutomotiveMirrorsElectronicsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_AutomotiveProductsMember_a1fc71ad-2d73-4eb0-9294-9c4d1f4288c6" xlink:to="loc_gntx_AutomotiveMirrorsElectronicsMember_901c0bde-53ee-46a3-bd4b-1c8bb69f0790" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_HomeLinkModulesMember_16ae91c8-e1d6-402c-a2d7-1a031824171f" xlink:href="gntx-20230930.xsd#gntx_HomeLinkModulesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_AutomotiveProductsMember_a1fc71ad-2d73-4eb0-9294-9c4d1f4288c6" xlink:to="loc_gntx_HomeLinkModulesMember_16ae91c8-e1d6-402c-a2d7-1a031824171f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OtherProductsMember_726390b0-27ff-4037-9f2e-a3d4ca4fc79b" xlink:href="gntx-20230930.xsd#gntx_OtherProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_99f3f241-d6bf-48bc-9045-04a0b2ab5bc9" xlink:to="loc_gntx_OtherProductsMember_726390b0-27ff-4037-9f2e-a3d4ca4fc79b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_FireProtectionProductsMember_b068bc19-d68d-46d2-858f-7da4ceacdfaf" xlink:href="gntx-20230930.xsd#gntx_FireProtectionProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_OtherProductsMember_726390b0-27ff-4037-9f2e-a3d4ca4fc79b" xlink:to="loc_gntx_FireProtectionProductsMember_b068bc19-d68d-46d2-858f-7da4ceacdfaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AerospaceProductsMember_cdc8a096-87fd-4270-8c0d-c46c458e87a3" xlink:href="gntx-20230930.xsd#gntx_AerospaceProductsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_gntx_OtherProductsMember_726390b0-27ff-4037-9f2e-a3d4ca4fc79b" xlink:to="loc_gntx_AerospaceProductsMember_cdc8a096-87fd-4270-8c0d-c46c458e87a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_aa018b32-df8a-405c-9f99-5e328055d67b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_2a8b5fe3-e05d-4a97-bd3b-4d9856ef63b6" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_aa018b32-df8a-405c-9f99-5e328055d67b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_aa018b32-df8a-405c-9f99-5e328055d67b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_aa018b32-df8a-405c-9f99-5e328055d67b" xlink:to="loc_us-gaap_SegmentDomain_aa018b32-df8a-405c-9f99-5e328055d67b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_4863935e-cb4c-4382-8406-a3ba125999cc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_aa018b32-df8a-405c-9f99-5e328055d67b" xlink:to="loc_us-gaap_SegmentDomain_4863935e-cb4c-4382-8406-a3ba125999cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_AutomotiveSegmentMember_e41a8d1c-0d3c-4207-b1f2-4a437c0fed4d" xlink:href="gntx-20230930.xsd#gntx_AutomotiveSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4863935e-cb4c-4382-8406-a3ba125999cc" xlink:to="loc_gntx_AutomotiveSegmentMember_e41a8d1c-0d3c-4207-b1f2-4a437c0fed4d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_OtherSegmentMember_e08b64f4-b5da-4ae3-a0c0-ec8521a04718" xlink:href="gntx-20230930.xsd#gntx_OtherSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4863935e-cb4c-4382-8406-a3ba125999cc" xlink:to="loc_gntx_OtherSegmentMember_e08b64f4-b5da-4ae3-a0c0-ec8521a04718" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/LeasesNarrativeDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#LeasesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/LeasesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_6de31164-67a0-4449-8a42-9e2cd16857f5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_c0840295-b442-4c04-8379-9b0f27fa4a1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6de31164-67a0-4449-8a42-9e2cd16857f5" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_c0840295-b442-4c04-8379-9b0f27fa4a1f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_87095c2c-cbf7-457b-8d8c-3d715f7b15c0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6de31164-67a0-4449-8a42-9e2cd16857f5" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageRemainingLeaseTerm1_87095c2c-cbf7-457b-8d8c-3d715f7b15c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_258426b2-6f89-42c8-98d2-b5f0ffd2cb0b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6de31164-67a0-4449-8a42-9e2cd16857f5" xlink:to="loc_us-gaap_OperatingLeaseWeightedAverageDiscountRatePercent_258426b2-6f89-42c8-98d2-b5f0ffd2cb0b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_18f00260-fc20-4fa2-8e62-edb93ea009eb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_6de31164-67a0-4449-8a42-9e2cd16857f5" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_18f00260-fc20-4fa2-8e62-edb93ea009eb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_178f4a2a-ea50-4850-a096-ecc964ed3c45" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_18f00260-fc20-4fa2-8e62-edb93ea009eb" xlink:to="loc_srt_RangeAxis_178f4a2a-ea50-4850-a096-ecc964ed3c45" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_178f4a2a-ea50-4850-a096-ecc964ed3c45_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_178f4a2a-ea50-4850-a096-ecc964ed3c45" xlink:to="loc_srt_RangeMember_178f4a2a-ea50-4850-a096-ecc964ed3c45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_635fb89b-eac3-401e-89d6-a22b184fb6e5" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_178f4a2a-ea50-4850-a096-ecc964ed3c45" xlink:to="loc_srt_RangeMember_635fb89b-eac3-401e-89d6-a22b184fb6e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_6221c8ba-c682-446b-9947-ceba7aff81c6" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_635fb89b-eac3-401e-89d6-a22b184fb6e5" xlink:to="loc_srt_MinimumMember_6221c8ba-c682-446b-9947-ceba7aff81c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_0a6a1e6e-b366-49ab-b306-518df2431b27" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_635fb89b-eac3-401e-89d6-a22b184fb6e5" xlink:to="loc_srt_MaximumMember_0a6a1e6e-b366-49ab-b306-518df2431b27" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.gentex.com/role/SubsequentEventDetails" xlink:type="simple" xlink:href="gntx-20230930.xsd#SubsequentEventDetails"/>
  <link:definitionLink xlink:role="http://www.gentex.com/role/SubsequentEventDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_17fc884a-e8af-4682-8940-370c59d71c24" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_9c801d3a-2682-4185-9109-1584df6d0871" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17fc884a-e8af-4682-8940-370c59d71c24" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_9c801d3a-2682-4185-9109-1584df6d0871" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_99ffe861-b40e-4154-a1a9-870f6d830201" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17fc884a-e8af-4682-8940-370c59d71c24" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_99ffe861-b40e-4154-a1a9-870f6d830201" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_BusinessCombinationEarnOutProvisionPeriod_f57e9b46-8ec7-4fd7-b8d7-bd8d0e2b0d3d" xlink:href="gntx-20230930.xsd#gntx_BusinessCombinationEarnOutProvisionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17fc884a-e8af-4682-8940-370c59d71c24" xlink:to="loc_gntx_BusinessCombinationEarnOutProvisionPeriod_f57e9b46-8ec7-4fd7-b8d7-bd8d0e2b0d3d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_eece8103-3c4f-42cd-ac1b-573d15015c41" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_17fc884a-e8af-4682-8940-370c59d71c24" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_eece8103-3c4f-42cd-ac1b-573d15015c41" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_9a9fc093-e281-486b-b4fb-d8439b02ca76" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_eece8103-3c4f-42cd-ac1b-573d15015c41" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_9a9fc093-e281-486b-b4fb-d8439b02ca76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9a9fc093-e281-486b-b4fb-d8439b02ca76_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_9a9fc093-e281-486b-b4fb-d8439b02ca76" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_9a9fc093-e281-486b-b4fb-d8439b02ca76_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0946aa3b-5d91-4a0a-8d7d-05fcf219825e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_9a9fc093-e281-486b-b4fb-d8439b02ca76" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0946aa3b-5d91-4a0a-8d7d-05fcf219825e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_gntx_ESightCorporationMember_f5415ea0-736a-41ad-ae24-085667ef26cf" xlink:href="gntx-20230930.xsd#gntx_ESightCorporationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0946aa3b-5d91-4a0a-8d7d-05fcf219825e" xlink:to="loc_gntx_ESightCorporationMember_f5415ea0-736a-41ad-ae24-085667ef26cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_8aba84da-a4de-4267-a201-dec5d02276a1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_eece8103-3c4f-42cd-ac1b-573d15015c41" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_8aba84da-a4de-4267-a201-dec5d02276a1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_8aba84da-a4de-4267-a201-dec5d02276a1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_8aba84da-a4de-4267-a201-dec5d02276a1" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_8aba84da-a4de-4267-a201-dec5d02276a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5a9ecccc-2639-4967-8a45-f3df6ab91881" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_8aba84da-a4de-4267-a201-dec5d02276a1" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5a9ecccc-2639-4967-8a45-f3df6ab91881" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_edaf911e-d370-4240-957c-bc745b6f03a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_5a9ecccc-2639-4967-8a45-f3df6ab91881" xlink:to="loc_us-gaap_SubsequentEventMember_edaf911e-d370-4240-957c-bc745b6f03a5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-roles-2023.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:type="arc" order="1"/>
  </link:definitionLink>
</link:linkbase>
