Bill Gates has sold 10 million shares in Microsoft this month, and a total of 90 million shares in the past 12 months, reducing his stock holdings by 13%.
Over the past two years, Gates has cut his interest in Microsoft by 22% through more than a dozen separate transactions, according to Information Week.
Gates now holds roughly 591 million Microsoft shares, about 7% of the company's 8.4bn shares, but still remains its largest single stockholder.
John Abbott, chief analyst at the 451 Group, said Gates' sale of shares did not come as a shock. "He stepped back from Microsoft a long time ago and is now completely focused on his philanthropic interests," he said.
Abbott said he expects a major reorganisation of top jobs at Microsoft, with new blood coming in to run the key business units - prompted by Microsoft's misreading of some of the biggest technology trends of recent times, most notably smartphones and tablets.
"Over the past year we've seen the departure of many of the Microsoft old guard - including chief software architect Ray Ozzie and server and tools chief Bob Muglia - in preparation for the reshuffle. Ballmer has been spearheading this effort and we don't see any change in his commitment to the company he's led for the past 11 years," he added.
Ballmer disposed of 49.3 million shares in the past week, bringing his total ownership to 358.9 million shares, or 4.2% of the company, according to a filing with the Securities and Exchange Commission. This was the first time he has sold Microsoft stock in seven years.