1200 V N-channel MOSFET — the high-voltage switching workhorse
The STFW8N120K5: Gate charge is 13.7 nC at 10 V.
At 2.5 A load, the 2 Ohm on-resistance drops about 12.5 W of conduction loss. The 48 W power dissipation ceiling (at case temperature) gives roughly 3.8x headroom at that current, so the part runs cool with a reasonable heatsink.
Package and mounting — TO-3PF through-hole
The TO-3PF is a fully isolated through-hole package — the metal tab is electrically isolated from the die, so no insulating pad is needed between the package and the heatsink.