The part of Idaho where you can build cheaply (Snake River Valley, flat-ish land) is a pretty long way from the major hydro dams on the Columbia. The Snake River dams generate almost zero electricity; they exist in order to allow barge transit for farm goods. So the "cheap power" benefit is out.

Micron is a giant in memory device manufacturing, but they don't do logic chips. Memory and logic manufacturing are pretty different, and get more and more different as you get to more and more bleeding-edge processes. Proximity to Micron is nice but not a huge benefit for a foundry.

Lastly, Idaho is gorgeous and the skiing is awesome, but it doesn't check the box for hipsters who want a coastal city. Don't blame me, I don't think this way. But a lot of people do. Anyways Idaho is definitely way beyond driving distance from Seattle.