Silicon Valley hasn’t been a prominent player in the pitched fundraising battle over whether to ban same-sex marriage in California — until now.

Google co-founder and president Sergey Brin this week donated $100,000 to the No on 8 campaign, while co-founder Larry Page added a $40,000 donation, a Mercury News analysis of state campaign finance records show. With the contribution, Brin matches talk show host Ellen DeGeneres for the largest individual donation during the campaign’s final weeks to oppose a proposed constitutional ban on same-sex marriage.

Google did not respond to initial requests for comment Thursday on the donations by Brin and Page, but the Mountain View Internet search giant is one of a very few Silicon Valley corporations officially on record opposing Prop. 8.

“While there are many objections to this proposition — further government encroachment on personal lives, ambiguously written text — it is the chilling and discriminatory effect of the proposition on many of our employees that brings Google to publicly oppose Proposition 8,” Brin wrote in an item he posted Sept. 26 on the official Google blog. “While we respect the strongly held beliefs that people have on both sides of this argument, we see this fundamentally as an issue of equality.”

The six-figure donations by DeGeneres and Brin were among a group of large donations from celebrities and other prominent figures that recently have flowed into Equality California, the lead organization battling Prop. 8. Marin County resident and “Indiana Jones” filmmaker George Lucas gave $50,000, while Lucasfilm donated an additional $50,000, both this week.

Actor T.R. Knight of “Grey’s Anatomy” gave two $50,000 donations, while Monica Rosenthal, an actress in the comedy series “Everybody Loves Raymond” and the wife of series writer and executive producer Phil Rosenthal, gave $25,000.

Those large donations are among $9.2 million in large donations received by Equality California ( www.noonprop8.com ) since Oct. 6, when the dueling Prop. 8 campaigns last filed their extensive fundraising reports, according to records filed with the California Secretary of State.

ProtectMarriage.com, the lead political organization supporting a ban on same-sex marriage, has raised about $1.7 million in large donations since Oct. 6, state records show.

Contact Mike Swift at (408) 271-3648 or at mswift@mercurynews.com.