U.S. Senate candidate Tom Campbell on Monday handed over his 2009 federal and state tax returns to the Mercury News for posting on its website.

"I favor transparency in government and in campaigns,'' Campbell said, emphasizing that he isn't calling on his Republican opponents, former Hewlett-Packard CEO Carly Fiorina and state Assemblyman Chuck DeVore, to follow his lead.

"All of the candidates have to make that decision for themselves,'' said Campbell, a former Silicon Valley congressman who is running neck-and-neck with Fiorina in the polls.

Representatives of the Fiorina and DeVore campaigns said late Monday that the candidates were open to the idea of releasing tax returns but made no specific promises.

Amy Thoma, Fiorina's press secretary, said Fiorina and her husband plan to release their 2009 returns "at a minimum,'' but it probably won't be until after the June 8 primary election because they have filed a tax extension this year.

In early January, when the Mercury News and the Bay Area News Group asked gubernatorial candidates to turn over 10 years of tax returns for posting on newspaper sites, Campbell was the only candidate who complied — albeit partially — by turning over his 2008 returns. A few days later, however, he switched to the Senate race in a move that rattled the state's election landscape.

The release of tax returns has since become a major issue in the governor's race. Republican billionaire Meg Whitman, GOP Insurance Commissioner Steve Poizner and the presumed Democratic candidate, Attorney General Jerry Brown, have all promised to release 25 years of returns. But so far they've been playing a game of "You go first!''

As he did for 2008, Campbell in tax year 2009 filed a separate return from his wife, showing an adjusted-gross income of $443,426.

He was paid $140,283 as a visiting law professor at Chapman University in Southern California. He also earned $12,922 in his final weeks as a professor at the Haas School of Business at UC Berkeley.

And he earned $713,105 as a director of the boards of credit card giant Visa International and FormFactor, a Livermore manufacturer of semiconductors and related devices. Campbell said he resigned from both boards after he decided to run for Senate.

Currently a resident of Irvine in Orange County, Campbell donated $600 to charity in 2009. He paid $147,236 in federal taxes and $39,690 in state taxes.

Campbell said he started filing separate tax returns from his wife in 2008, a move that will allow him to protect his wife's privacy as he releases tax returns showing his sources of income.

"She's never chosen to run for office,'' he said with a laugh.

Contact Ken McLaughlin at 408-920-5552.