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

March 11, 2016

Date of Report (Date of earliest event reported)

ON Semiconductor Corporation

(Exact name of registrant as specified in its charter)

(602) 244-6600

(Registrant’s telephone number, including area code)

Not applicable

(Former name or former address, if changed since last report.)

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 following provisions:

Item 1.01. Entry Into a Material Definitive Agreement.

Supplemental Indentures

On March 11, 2016, ON Semiconductor Corporation (the “Company”) and the Additional Guarantors (as defined herein) entered into a Supplemental Indenture (the “1.00% Notes Supplemental Indenture”) with Wells Fargo Bank, National Association, as trustee (the “1.00% Notes Trustee”), to that certain Indenture (the “1.00% Notes Indenture”), dated as of June 8, 2015, among the Company, the guarantors party thereto and the 1.00% Notes Trustee, pursuant to which the Company has issued 1.00% Convertible Senior Notes due 2020 (the “1.00% Notes”). Pursuant to the 1.00% Notes Supplemental Indenture, Sensor Holding Corporation, Sensor Intermediate Holdings Corp., Truesense Imaging, Inc., Image Sensor Technologies RE Corp. and AMI Acquisition LLC (the “Additional Guarantors”), all of which are domestic subsidiaries of the Company, guaranteed the Company’s obligations under the 1.00% Notes Indenture and the 1.00% Notes.

On March 11, 2016, the Company and the Additional Guarantors entered into a Supplemental Indenture (the “2.625% Notes Supplemental Indenture”) with Deutsche Bank Trust Companies Americas, as trustee (the “2.625% Notes Trustee”), to that certain Indenture (the “2.625% Notes Indenture”), dated as of December 15, 2011, among the Company, the guarantors party thereto and the 2.625% Trustee, pursuant to which the Company has issued 2.625% Convertible Senior Subordinated Notes due 2026, Series B (the “2.625% Notes”). Pursuant to the 2.625%% Notes Supplemental Indenture, the Additional Guarantors guaranteed the Company’s obligations under the 2.625% Notes Indenture and the 2.625% Notes.

Joinder to Amended and Restated Credit Agreement

On March 15, 2016, the Additional Guarantors entered into a Joinder (the “Joinder”) to that certain Amended and Restated Guaranty, dated as of October 10, 2013, among the Initial Guarantors (as defined therein) and JPMorgan Chase Bank, N.A., as administrative agent (the “Administrative Agent”). Pursuant to the Joinder, the Additional Guarantors guaranteed the obligations of Semiconductor Components Industries, LLC, a wholly-owned subsidiary of the Company (“SCILLC”), under that certain Amended and Restated Credit Agreement, dated as of October 10, 2013, among SCILLC, the Company, the lenders from time to time party thereto, the Administrative Agent, Bank of America, N.A., The Royal Bank of Scotland plc, and Sumitomo Mitsui Banking Corporation, as co-syndication agents, and Morgan Stanley MUFG Loan Partners, LLC, Barclays Bank plc and Fifth Third Bank, as co-documentation agents.

The foregoing descriptions of the 1.00% Notes Supplemental Indenture, the 2.625% Notes Supplemental Indenture and the Joinder do not purport to be complete and are qualified in their entirety by reference to the full and complete terms of the 1.00% Notes Supplemental Indenture, the 2.625% Notes Supplemental Indenture and the Joinder, which are filed as Exhibit 4.1, Exhibit 4.2 and Exhibit 10.1 to this Current Report on Form 8-K, respectively, and are incorporated herein by reference.

Item 9.01. Financial Statements and Exhibits.

(d) 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.

EXHIBIT INDEX