In a letter to shareholders, Bostock, along with board members Vyomesh Joshi, Arthur Kern and Gary Wilson have announced they will not seek re-election to the board this year.
The digital media company has not announced a new chairman.
Bostock leaves amid a major shakeup to the company’s leadership. This month it appointed Scott Thompson, former president of PayPal as its new chief executive, after Carol Bartz was dismissed in September last year.
Shortly after Thomspon joined, Jerry Yang, co-founder of Yahoo, resigned from the board.
Marketing recently revealed a major restructure to its European marketing department, as part of its move to shift its global marketing function to the regions.
The shakeup saw the departure of James Tipple, vice president of marketing EMEA, and Andrew Cocker, European marketing director departed.
Robert Bridge, former business-to-business marketing director for EMEA, has been promoted to the role of senior director and head of marketing for the region.
This month Yahoo reported a 4% slip in global revenues, hit by a decline in search and ad revenues.
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