Redmond, Wash. ? Microsoft Corp. Chairman Bill Gates announced Thursday that he would transition from day-to-day responsibilities at the company he co-founded to concentrate on the charitable work of the Bill & Melinda Gates Foundation.

Gates will continue on as the company’s chairman after transferring his duties over a two-year period.

“This was a hard decision for me,” said Gates, who founded the world’s largest software company with childhood friend Paul Allen. “I’m very lucky to have two passions that I feel are so important and so challenging. As I prepare for this change, I firmly believe the road ahead for Microsoft is as bright as ever.”

Microsoft’s Chief Technical Officer Ray Ozzie immediately will assume Gates’ title as chief software architect and begin working side by side with Gates on overseeing all software technical design.

Chief Technical Officer Craig Mundie immediately takes the new title of chief research and strategy officer and will work with Gates in those areas. Mundie also will partner with general counsel Brad Smith to guide Microsoft’s intellectual property and technology policy efforts.

The news was announced after financial markets closed. Earlier, shares in Microsoft rose 19 cents, or 0.87 percent, to close Thursday at $22.07 on the Nasdaq Stock Market. Shares gained 5 cents in after-hours trading.