Hennessy, 65, a computer scientist with expertise in chip design and deep connections in Silicon Valley, joined Google's board in 2004 months before the company went public. He was dean of Stanford's engineering school when students Sergey Brin and Larry Page developed Google and was an early tester of their technology. Hennessy will be non-executive chairman, unlike Schmidt, who was an Alphabet employee.

"It's a privilege!" Hennessy said by email about the new role.

Shirley Tilghman also announced her retirement from the Alphabet's board effective Feb. 15, the company said in the U.S. Securities and Exchange Commission filing. She did not respond to a request to comment.

Schmidt stepped down in January, ending a 17-year run in which he played a central role in building a promising startup called Google into a global technology powerhouse. He remains a board member and adviser on technical and science issues.

Hennessy's chairmanship begins at a time when lawmakers, privacy critics and other groups fear that Google may have too much control over how people connect with each other in the digital age. It has been blasted for allowing extremist videos to stream on YouTube and misleading news to lead Google search results.

Rivals in Alphabet's biggest business, online advertising, have complained about anti-competitive practices. Questions about collection of user data are omnipresent, especially as Alphabet develops cars, smart speakers and facial recognition software.

Hennessy presided over Stanford as it became more academically competitive with Ivy League schools such as Harvard and Yale universities. He saw its endowment surge during boom years in Silicon Valley, where the school is located.

As a Stanford researcher, Hennessy co-founded chip design startup Mips Computer Systems, which was acquired by Silicon Graphics International in 1992. He has been lead independent director at Google and Alphabet since 2007.

Schmidt came to Google as a veteran tech executive to provide "adult supervision," as he, Page and Brin have described it. He served as chairman from 2001 to 2004 and from 2007 through January.

Schmidt led the company's involvement in industry disputes and public policy fights around the world. He oversaw Google's 2004 initial public offering and its reorganization under the Alphabet holding company in 2015.

Over the last two years, Chief Financial Officer Ruth Porat, Google Chief Executive Sundar Pichai, YouTube CEO Susan Wojcicki, and Diane Greene, senior vice president of Google's enterprise business, have taken on a greater role as the public faces of the company.

(Reporting by Paresh Dave; Editing by Richard Chang and Lisa Shumaker)

By Paresh Dave