Despite their relative size and prominence, Taiwanese EMS firms not named Foxconn don’t get much play in the US. But today’s deal is a doozy: Advanced Semiconductor Engineering, a provider of semiconductor manufacturing and IC packaging services, along with its two subsidiaries, has offer to acquire all outstanding common shares of Universal Scientific Industrial Co., Ltd. in a cash and stock deal valued at about $571 million.

USI is, of course, the world’s 24th largest – and Taiwan’s third largest, after Foxconn and Orient Semiconductor – provider of EMS services. It had 2008 EMS sales of $490.4 million, and EMS work makes up about 25% (or about $318 million) of its overall sales so far this year.

ASE and its subsidiaries already own 18.2% of USI’s outstanding common shares. Assuming it goes through, this will create a packaging, test and board assembly monster. Advanced Semiconductor Engineering already is the world’s largest test and packaging house. ASE’s revenues year-to-date are $1.84 billion; USI’s are $1.27 billion.

That’s some serious vertical integration.