UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 17, 2012

GENTHERM INCORPORATED

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (248) 504-0500

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the follow provisions:

Sections 1. Registrant’s Business and Operations

Item 1.01 Entry into a Material Definitive Agreement

On March 30, 2011, Gentherm Incorporated (“Gentherm”), together with its subsidiary Gentherm Europe GmbH (“Gentherm Europe”) entered into a Credit Agreement (the “U.S. Credit Agreement”) with the Lenders party thereto, Bank of America, N.A., as Administrative Agent, Swing Line Lender and L/C Issuer, and Merrill Lynch, Pierce, Fenner & Smith Incorporated, as sole lead arranger and sole book manager (collectively the “Lenders”).

On December 17, 2012, Gentherm, Gentherm Europe and the Lenders entered into a Fifth Amendment to Credit Agreement (the “Material Amendment”). The material provisions of the Material Amendment are described herein. The Material Amendment included an extension of the availability period for draws under the term loan available to Gentherm Europe from January 1, 2013 to June 30, 2014. Approximately $40 million is currently available under this loan to fund the potential tender of shares of W.E.T. Automotive Systems AG (“W.E.T.”) in connection with the Domination and Profit and Loss Transfer Agreement. The Material Amendment also increased the amount available under the Revolving Line Credit (as defined in the Credit Agreement) from $25 million to $30 million and reduced the Applicable Rates for Eurocurrency Rate Loans and Letters of Credit (as each term is defined in the Credit Agreement) by 0.75% to a range of 1.75% to 2.50% and reduces the Applicable Rates for Base Rate Loans (as defined in the Credit Agreement) by 0.75% to a range of 0.75% to 1.50%. Actual Applicable Rates applied to outstanding Loans (as defined in the Credit Agreement) and Letters of Credit continue to be determined based upon the Consolidated Leverage Ratio (as defined in the Credit Agreement) of Gentherm.

W.E.T. and W.E.T. Automotive Systems LTD., a Canadian corporation (the “Canadian Borrower”) are parties to a Credit Agreement dated March 30, 2011 (the “German Credit Agreement”). On December 17, 2012, W.E.T., the Canadian Borrower and the other parties to the German Credit Agreement entered into a Fifth Amendment to the German Credit Agreement (the “German Amendment”). The material provisions of the German Amendment are described herein. The German Amendment included an increase the amount available under the Revolving Line Credit (as defined in the German Credit Agreement) from €10 million to €30 million and reduces the Applicable Rates for Eurocurrency Rate Loans and Letters of Credit (as each term is defined in the German Credit Agreement) by 0.75% to a range of 1.75% to 2.50% and reduces the Applicable Rates for Base Rate Loans (as defined in the German Credit Agreement) by 0.75% to a range of 0.75% to 1.50%. Actual Applicable Rates applied to outstanding Loans (as defined in the German Credit Agreement) and Letters of Credit continue to be determined based upon the Consolidated Leverage Ratio (as defined in the German Credit Agreement) of W.E.T.

Copies of the Material Amendment and the German Amendment are attached as Exhibits 10.1.5 and 10.2.5 to this Current Report on form 8-K, and the above description of the material terms of such documents is qualified in its entirety by reference to such exhibits, which are incorporated herein by reference.

Sections 2-8. Not applicable.

Section 9. Financial Statements and Exhibits.

Item 9.01 Financial Statements and Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: December 21, 2012

Exhibit Index