In afterhours activity on the Island trading network, shares of Microsoft traded between 104 and 108, but generally not veering far from Microsoft's Thursday close of 107 13/16.
Ballmer will join the Microsoft board on Jan. 27. Gates will remain chairman of Microsoft and take the title of chief software architect.
"I certainly enjoy being CEO," Gates said Thursday. "The business challenges, the organizational challenges, those are things I dove into and learned a lot about. However, what I really enjoy the most, and what I'm getting back to ... is working with the product group."
Gates gradually has been moving away from running Microsoft's daily operations. Thursday's move lets Gates focus almost entirely on technology development, the company said. Microsoft is focusing on providing Internet-based software services, executives said.
Having Ballmer as CEO likely won't change much about the way Microsoft does business. Microsoft's board two years ago began talking about a reduction in Gates' involvement in the company's day-to-day operations. The appointment of Steve Ballmer as president about a year and half ago was the first step in that plan.
In the last two years, shares of Microsoft have risen 232 percent on a split-adjusted basis. The Nasdaq Composite Index, which is largely driven by large cap tech companies such as Microsoft, is up 162 percent over the same period.
Thursday's move comes on the heels of media reports that the U.S. Department of Justice will push for a breakup of Microsoft as a remedy for the government's antitrust case. But Gates told CNBC that the CEO change was "absolutely not" a response to the antitrust case.
The announcement also comes just days before Microsoft's scheduled quarterly report next Tuesday. The company last month appointed John Connors to replace Greg Maffei as chief financial officer.
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