I've been pushing (ie, blowing up) come Cree SiC power fets, the 1200 volt 280 mohm part in TO247. It sure looks like thermal runaway.
Just for fun I ground one down.
No wonder it blows up. The actual chip is tiny, so all the heat is in one spot. Why bother to put it in that giant TO247 package?
A healthy mosfet die would use most of the available area.
I've ordered some ST SiC parts. They have similar capacitance and twice the Rds-on, but Ron barely changes with temperature. The Cree Rds-on takes off radically with temperature, so the ST wins above150C.
I'll gring down an ST part too.
We are considering getting an x-ray machine. It will inspect BGA solder joints and will count parts, loose in trays or on reels. Engineering could use it to snoop inside parts like this, maybe.