MOSFETs (both Si/SiC and more recent GaN) switching transistors may be made on special (Epi or Sapphire) wafers, but the Fabs are very old school (e.g. 2-6in vs 12in for CMOS) and the process geometries are practically neolithic (e.g. 90s). Processing equipment is more limited by the lack of desire to build or support something so old. Die sizes are also quite reasonable (e.g. 4kW/cm2) However, there is still enormous capacity for processing them around the world (both in US/EU, and around Asia).

Perhaps, for the new GaN on Sapphire wafers there could be a significant manufacturing limit? Mostly, those are used for Blue LEDs today.