900 V N-channel — Zener-protected gate for field swaps
The Z suffix means the gate is Zener-protected — a detail that matters when you are swapping this part on site without an ESD bench: the internal clamp absorbs gate overvoltage that would punch through a standard MOS gate.
6.5 Ohm Rds(on) — conduction loss on a TO-220 tab
Maximum on-resistance is 6.5 Ohm at 1.05 A drain current with 10 V gate drive. That is the number you use for heatsink sizing: at 2.1 A the conduction loss hits about 14 W, and the TO-220 package is rated for 70 W dissipation at the case — plenty of headroom if you bolt it to a decent heatsink.
-55 to 150°C junction — no temperature derating guesswork
The 70 W power dissipation rating is at 25°C case — derate linearly above that per the datasheet curve, but the headroom is generous for a 2.1 A device.
No last-time-buy clock is ticking, no broker premium needed. The base product number is STP2NK90; the Z variant adds the Zener clamp but shares the same TO-220 footprint and pinout.