As filed with the Securities and Exchange Commission on June 7, 2017

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 20549

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

DexCom, Inc.

(Exact name of Registrant as Specified in Its Charter)

6340 Sequence Drive

San Diego, California 92121

(Address, including zip code, of Registrant’s principal executive offices)

Amended and Restated 2015 Equity Incentive Plan

(Full Title of the Plans)

Kevin Sayer

Chief Executive Officer and President

c/o DexCom, Inc.

6340 Sequence Drive

San Diego, California 92121

(858) 200-0200

(Name, Address and Telephone Number of Agent For Service)

Copies to:

Robert A. Freedman, Esq.

Michael A. Brown, Esq.

Fenwick & West LLP

801 California Street

Mountain View, CA 94041

(650) 988-8500

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act. (Check one):

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to 7(a)(2)(b) of the Securities Act.  ☐

CALCULATION OF REGISTRATION FEE

STATEMENT PURSUANT TO GENERAL INSTRUCTION E TO FORM S-8

REGISTRATION OF ADDITIONAL SECURITIES

Pursuant to General Instruction E of Form S-8, DexCom, Inc. (the “Registrant”) is filing this Registration Statement with the Securities and Exchange Commission (the “Commission”) to register 3,600,000 additional shares of common reserved for issuance upon the exercise of stock options and the settlement of restricted stock unit awards under the 2015 Plan to be granted by the Registrant.

This registration statement (the “Registration Statement”) hereby incorporates by reference the contents of Registrant’s earlier registration statement on Form S-8 (registration number 333-204699) filed with the Commission on June 3, 2015. In accordance with the instructional note to Part I of Form S-8 as promulgated by the Commission, the information specified by Part I of Form S-8 has been omitted from this Registration Statement.

Item 8. Exhibits.

The following exhibits are filed herewith:

SIGNATURES

Pursuant to the requirements of the Securities Act, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of San Diego, State of California, on this 7th day of June, 2017.

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS that each individual whose signature appears below constitutes and appoints Kevin Sayer and Kevin Sun, and each of them, his or her true and lawful attorneys-in-fact and agents with full power of substitution, for him and in his name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this Registration Statement on Form S-8, and to file the same, with all exhibits thereto and all documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done with respect to this Registration Statement, including post-effective amendments, as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or his substitute or substitutes, may lawfully do or cause to be done or by virtue hereof.

Pursuant to the requirements of the Securities Act, this Registration Statement has been signed by the following persons in the capacities and on the date indicated.

Exhibit Index