The 3.5 Ohm figure is moderate for a 3 A-rated 800 V MOSFET — expect conduction losses around 1.6 W at 1 A rms, which the 80 W power dissipation capability (at case temperature) can handle with adequate heatsinking.
Gate charge and input capacitance — switching speed check
Total gate charge is 22.5 nC at 10 V, and input capacitance is 575 pF at 25 V drain-source.
DPAK footprint and thermal path
The DPAK (TO-252) package has a metal tab on the top that is the drain connection. In a typical layout, the tab is soldered to a copper pad on the PCB — that pad area sets the junction-to-ambient thermal resistance. For the 80 W dissipation rating at case temperature, a proper thermal pad with vias to an inner-layer copper plane is expected.
Temperature range and compliance
The part is ROHS3 compliant.