Yahoo co-founder and onetime CEO Jerry Yang resigned Tuesday from the company's board as well as from the board of China's Alibaba Group, where Yahoo has a 44 percent interest.

The time has come for me to pursue other interests outside of Yahoo, the Taiwan-born Stanford University computer graduate said. Yang, 43, expressed confidence in new CEO Scott Thompson, recruited from eBay's PayPal unit this month.

Yang, who co-founded Yahoo with fellow student David Filo, now 45, in 1995, didn't indicate future plans. A billionaire based on his Yahoo shares, Yang might turn to other activities.

Yahoo shares rose in after-hours Tuesday trading to $15.99, up 56 cents. The Sunnyvale, Calif.-based search engine has a market capitalization of $19 billion.

Before Thompson's appointment, there had been industry speculation that Yang might participate in some kind of private equity buyout of the company. Thompson said Yahoo is still exploring ways to sell its shares in Alibaba as well as Yahoo Japan, where the company also holds a minority stake.