Microsoft Corp. /zigman2/quotes/207732364/composite MSFT +1.02% co-founder Bill Gates is stepping down from the boards of the software company and of Berkshire Hathaway Inc. /zigman2/quotes/208872451/composite BRK.A +0.58% [brk.b], according to a press release and a filing late Friday. Microsoft said in a statement that Gates will dedicate more time to philanthropy, and continue to serve as technology adviser to Chief Executive Satya Nadella. With Gates's departure, Microsoft's board will have 12 members. In a filing, Berkshire only said that Gates, who has served as director since 2004, will retire from the board. Ken Chenault, former American Express Co. /zigman2/quotes/203805826/composite AXP -3.05% chief executive, was nominated to fill Gates's vacancy. Shares of Microsoft fell 3% in the extended session Friday after ending the regular trading day up 14%.