An Apple spokesman has confirmed to Forbes that the company has agreed to buy the boutique microprocessor design specialists PA Semi. Known for their expertise in low-power mobile processors, PA Semi was founded in 2003 by Dan Dobberpuhl, a lead designer on early ARM chips; the company currently employs 150 people. Speculation is rife that PA Semi chips will now find their way into the iPhone and future portable devices by Apple.

Although neither company would comment on the value of the deal, a person familiar with the arrangement has suggested it was a cash sale worth $278 million. The buy has come as a surprise to many analysts, who expected Apple’s headline-grabbing relationship with Intel to see future mobile devices using the chip company’s own Atom platform, itself a low-power design. It’s been suggested that Apple’s acquisition is in part to further seal off the potential of upcoming products leaking, which has historically plagued the run-up to each eagerly-anticipated launch. Negotiations took mere weeks, although prior to the Intel deal Apple and PA Semi were in talks which then fell through.

This doesn’t mean, of course, that we’ll see a PA Semi chip in the 3G iPhone; the deal is too recent for that. But given the ongoing rumors of an Apple UMPC – possibly in the form of a larger, maybe QWERTY-equipped iPod Touch – and the iPhone’s further blurring of the smartphone, MID and UMPC niches, it’s unsurprising that the company is looking for highly efficient mobile processors. According to Forbes, Apple plans to continue to supply and support existing PA Semi customers, but keep future chips exclusively for itself.