The company made the donation on Friday to Washington Families Standing Together, a group supporting the law, which gives registered couples the same state-provided benefits as married couples.
Microsoft faced intense criticism in 2005 after taking a neutral stance on a state bill banning discrimination against gays and lesbians, which it had supported in the past.
At the time, the company was on the receiving end of pressure from Ken Hutcherson, pastor at Antioch Bible Church in Redmond and outspoken gay-rights critic. Chief Executive Steve Ballmer later changed the company’s position to support the bill.
Read more at the Seattle Times.