Thanks, as you now, the MOSFET datasheets and App Notes give the Abs Max Tjunction, ..... can be anywhere between 125degC and 175degC.
But allowing that will mean a short lived SMPS.
It is known (but not written publicly anywhere), that you should not run a MOSFET junction above 105degC if you want a reasonably long lasting
SMPS.
As you know, we simply cannot make MOSFETS physically rigid and rugged and robust like the stantion supports in big buildings or big bridges...the MOSFET internal structures, are, of necessity, highly delicate structures, and repeated expansion/contraction will kill them prematurely. The interfaces between the fine structures of a MOSFET are just too fine.....they will be busted by repeated expansion/contraction....As i discuss, you are never going to build the inner support structure of a skyscraper, etc etc, with "MOSFET material".
The 105degC figure, is the "in_the_club" figure, that you hear over and over.
It makes sense too...those internal structures are extremely fine and delicate....necessarily so.
As i discuss, there are no public books or websites that will tell you this...it is just an "in_the_club" fact.
There is no way that the "engineer_in_the_street" can calculate it either.