Christensen, who also helped start the Symbian consortium, joined Microsoft in September 2000 to spur the company's efforts to create software for handheld computers and cell phones.
The unit is still unprofitable, but sales have been growing of late as Windows Mobile 2003 Pocket PC-based devices have gained ground in the handheld market. Also, the first products using Microsoft's Smartphone 2003 operating system are just coming to market. For example, AT&T Wireless last month started selling a Motorola-made phone using Microsoft's software.
Christensen is leaving to join a Silicon Valley-based mobile device start-up that will also have offices in Christensen's native Denmark. He will work at Microsoft through Dec. 1 and will begin at the unnamed start-up on Jan. 1, according to a Microsoft representative. Christensen, corporate vice president of Microsoft’s Mobile Devices Marketing Group, told his team of his plans Wednesday night, the representative said.
"Juha has done great work at Microsoft, creating excellent business momentum for our Mobile Devices Division," the company said in a statement. "We're very sorry to see him go, but are thrilled with opportunities to work with him as a partner moving forward in his new ventures."
Last quarter, Microsoft's mobile and embedded devices unit, which includes the handheld and smart-phone business, had revenue of $53 million, up from $28 million a year ago.
Microsoft did not immediately name a successor for Christensen. Those who had reported to him will report to Pieter Knook, senior vice president of Microsoft's mobile and embedded devices unit.
The Symbian consortium, which Christensen helped to launch, is one of Microsoft's key rivals in the market for operating systems that can power advanced cell phones.