Bostock is departing along with Vyomesh Joshi, Arthur Kern and Gary Wilson. In a letter released to shareholders Tuesday, Roy Bostock wrote that these departures are voluntarily.
The shake-up continues a drastic makeover of Yahoo's leadership during the past month as the company tries to win back investors frustrated with years of broken turnaround promises.
After Yahoo hired former PayPal executive Scott Thompson as its CEO a few days into the new year, co-founder Jerry Yang resigned from the board and severed all other ties with the company, which he helped start in 1995.
Now Bostock is departing after four years as chairman. Many Yahoo shareholders have been clamoring for Bostock to step down since the company balked at a $47.5 billion, or $33 per share, takeover offer from Microsoft Corp. in 2008. Yahoo's stock hasn't traded above $20 in nearly 3 1/2 years.
Shares of the company ticked down slightly in afterhours trading. (Click here for latest quote.)
Along with the mass exodus, Yahoo announced the appointment of two new directors: Alfred Amoroso, former CEO of Rovi, and Maynard Webb Jr., a former eBay executive who most recently was CEO of LiveOps.