Chips aren't a single piece of Si or SiC crystal, but a superbly complicated arrangement of doped regions, insulating, metal and plating layers, so the melting

Chips aren't a single piece of Si or SiC crystal, but a superbly complicated arrangement of doped regions, insulating, metal and plating layers, so the melting point of the base crystal doesn't matter here (Si melts at ~1500 °C, C depends, and SiC seems to sublime at very high temperatures like carbon, instead of melting - corrections welcome). The limit to sustained high-temperature operation of ICs is due to all of these things starting to diffuse around and getting into places they're not supposed to be.