Best way to segment customers in the semiconductor space?

Firmographic alone won't cut it in semiconductors — you'll want to layer in needs-based or application-based segmentation on top. Think end-market (automotive vs. consumer electronics vs. industrial) plus design cycle stage, since a company in early R&D buys very differently than one in mass production. I'd start by mapping those two dimensions against your firmographic data and you'll see much cleaner clusters.