Walker reported that his campaign raised $8.2 million from January through June, compared with $3.6 million for Burke. Walker had $7.6 million cash on hand while Burke had $2.5 million.
Both campaigns reported their numbers nearly two weeks before the July 21 deadline. Burke put hers out first and Walker followed two hours later.
Walker, a potential 2016 Republican candidate for president, is seeking a second term in office while it is Burke's first campaign for a statewide office.
Burke gave her campaign $400,000 out of her own pocket shortly after getting into the race in October, but she has not contributed any more since then, said her spokesman, Joe Zepecki.
"Due to the overwhelming support Mary has received, there has been no need for additional contributions to this point," Zepecki said. "As she has said all along, she is committed to doing more and will do more before the race is over."
Walker's campaign manager Stephan Thompson said Walker's totals show the "extraordinary enthusiasm" behind his campaign.
Burke's estimated $2.5 million cash on hand heading into the four months of the campaign is about the same as what Walker had in 2010 when he ran for the first time. That year Democrat Tom Barrett had $2.9 million cash on hand at this point. And in 2006, Republican challenger Mark Green had $3.1 million, while incumbent Gov. Jim Doyle had $5.1 million.
While both Walker and Burke were raising millions for the race, spending by independent outside groups was expected to greatly eclipse anything the candidates put into the election this year.
Total spending in Walker's first run for governor in 2010 eclipsed $36 million, the highest ever for a governor's race. That record was shattered in Walker's recall election less than two years later, when spending reached $81 million. Normal campaign finance limits did not apply during much of that race due to rules governing recall elections.
Burke's early release of her fundraising totals comes the day after Walker launched an attack ad that accused her of wasting $12.3 million of taxpayer dollars while serving as secretary of the state Commerce Department in 2006. Burke also launched her own positive autobiographical television ad on Wednesday.
The Walker spot focused on Burke's role as state commerce secretary in awarding the $12.3 million grant designed to help lure Illinois-based Abbott Laboratories north to Wisconsin. While the project was touted at the time as having the potential to add 2,400 jobs to Wisconsin, Abbott has not developed the land or created any jobs.
The federal government last year ordered the state to repay the U.S. Department of Housing and Urban Development because the $12.3 million award did not meet HUD's national objectives or provide a public benefit.
Even though Walker used the grant to attack Burke, his own administration defended the award in a letter sent to HUD on May 29, 2013. In that letter, a Walker official said the acquisition of the land in question led to economic development and job creation, even though Abbott Labs had not done anything.