Ballmer did provide a timeframe for Srivastava's departure, and was vague about the reasons behind it.
"Windows Azure is in a great place, and Amitabh is ready to move to a new phase in his career. He has done stellar work for the company and I will work to ensure a smooth transition with the Windows Azure team," said Ballmer.
It's thought that Srivastava's exit is connected to Microsoft's announcement that company veteran Satya Nadella would replace Bob Muglia as head of Server and Tools. Ballmer effectively fired Muglia from the post, and many observers believed Srivastava was in the running for the job.
Srivastava is a 14-year Microsoft veteran and one of the few execs there to receive the Technical Fellow designation. Among other things, he co-led the build out of Windows Azure, the online version of the Windows operating system that Microsoft is counting on as the foundation of its cloud computing efforts.
Ballmer's shakeup of his company's top ranks may not be over. With Microsoft struggling to keep up in new markets like tablets, phones, search, and social networking, Ballmer is said to be looking for a new crop of senior lieutenants whose roots are in programming and engineering, as opposed to sales and marketing.
The reshuffling could address concerns that Microsoft has lost its edge as an innovator and that it's overly focused on promoting existing technologies rather than building new ones. The Kinect motion controller for the Xbox was one of the company's few successes in 2010, a year in which it suffered reversals in the tablet and cell phone markets.
Microsoft shares were off 1.9%, to $27.43, just before the closing bell in Thursday trading.