The STF5N95K3 is an N-channel MOSFET in a TO-220 Full Pack (TO-220FP) package, rated for 950 V drain-to-source voltage and 4 A continuous drain current.
On-resistance and gate charge — sizing the drive and thermal budget
At 4 A the Rds(on) will be higher — budget for conduction loss using the normalised Rds(on) vs. Id curve in the datasheet. Total gate charge is 19 nC at Vgs = 10 V, which keeps the gate drive energy low enough for a simple bootstrap or transformer-coupled driver at switching frequencies up to 100 kHz or so. Input capacitance Ciss is 460 pF at Vds = 25 V. Combined with the 19 nC gate charge, the gate driver load is light.