Rambus (RMBS) S-8Registration of securities for employees

Exhibit 5.1

May 29, 2020

Rambus Inc.

1050 Enterprise Way, Suite 700

Sunnyvale, California 94089

Re: Registration Statement on FormS-8

Ladies and Gentlemen:

We have examined the Registration Statement on FormS-8 (the “Registration Statement”) to be filed by Rambus Inc., a Delaware corporation, with the Securities and Exchange Commission on or about the date hereof, in connection with the registration under the Securities Act of 1933, as amended, of (i) 7,800,000 shares of common stock, par value $0.001 per share (“Common Stock”) reserved for issuance pursuant to the Company’s 2015 Equity Incentive Plan and (ii) 2,000,000 shares of Common Stock, reserved for issuance pursuant to the Company’s 2015 Employee Stock Purchase Plan (which plans are referred to herein as the “Plans” and which shares of Common Stock are referred to herein as the “Shares”).

It is our opinion that the Shares, when issued and sold in the manner referred to in the Plans and pursuant to the agreements that accompany the Plans, will be legally and validly issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Registration Statement, and further consent to the use of our name wherever appearing in the Registration Statement and any amendments thereto.