It carries a 320 mOhm maximum on-resistance at 6 A with 10 V gate drive.
With a typical gate charge of 30 nC at 10 V and input capacitance of 960 pF at 50 V drain bias, this MOSFET is suited for moderate-frequency hard-switched converters — think flyback or PFC stages in the 50–150 kHz range. The 25 W power dissipation limit in the TO-220FP package is the thermal ceiling; the full-pack construction means the junction-to-case thermal path runs through the epoxy back, not a metal tab, so derate the continuous current if the heatsink interface isn't well-greased.
Finding a replacement
With the STF13NM50N now obsolete, the BOM needs a pin-compatible drop-in. The TO-220FP footprint is the constraint — a standard TO-220 metal-tab part won't fit the same hole pattern without an insulator. ST's MDmesh series has newer generations (MDmesh V, MDmesh M2) that offer lower Rds(on) and gate charge in the same package outline, though the exact order code depends on the current and voltage class your design requires. A same-function alternative from another manufacturer would need to match the TO-220FP package, 500 V minimum Vds, and 12 A continuous rating.