In 2021, Sonsini was chosen to serve as chair of the board of trustees at Santa Clara University.
He ultimately chose to stay in Northern California on the advice of his securities law professor.
He later counseled hardware firms such as Sun Microsystems, Apple Computer, Silicon Graphics and Seagate Technology and software companies such as Novell, Sybase, WordPerfect and VMware.
[6] He has served as an advisor to many of the key figures in Silicon Valley history, including Steve Jobs, and the principals of Google and Hewlett-Packard.
In 2006, he was called to testify in front of a subcommittee of the U.S. House Energy and Commerce Committee to answer questions about an investigation by Hewlett-Packard into leaks from its board of directors, in which it was alleged that private detectives hired by the chairperson illegally obtained private phone records of some of the company's board members.