The STMicroelectronics STFI8N80K5 is an 800 V, 6 A N-channel MOSFET from the SuperMESH5™ series, built on ST's avalanche-rugged strip layout technology. This part targets high-voltage offline power supplies, flyback converters, and auxiliary switched-mode circuits where 800 V blocking and moderate current (6 A) are needed, and where through-hole mounting suits the assembly flow.
950 mOhm on-resistance — what it means for conduction loss
At 6 A full load, expect about 5.7 W dissipation from the channel alone, before switching losses. That puts the 25 W package power limit into perspective — the thermal margin is comfortable for a 6 A continuous load in a well-ventilated design, but a heatsink is mandatory for anything above light duty.
Gate charge and input capacitance — switching speed considerations
With a typical gate charge of 16.5 nC at 10 V and input capacitance of 450 pF at 100 V drain-source, this MOSFET is not a high-speed switcher but is well matched to 50–150 kHz hard-switched converters. The gate drive voltage is specified at 10 V for minimum Rds(on); driving it with a 5 V logic-level signal will roughly double the on-resistance, so plan the gate driver rail accordingly.
For new designs, select a current-production 800 V N-channel MOSFET in a TO-262-3 or equivalent through-hole package.