30 V, 4.2 mOhm N-channel — the low-side workhorse now obsolete
The STD95N3LLH6 is an STMicroelectronics N-channel power MOSFET from the DeepGATE™ and STripFET™ VI series. The gate threshold is 2.5 V max at 250 µA, and the total gate charge is 20 nC at 4.5 V.
STMicroelectronics no longer manufactures this exact order code. A cross-reference search against the 30 V, DPAK, N-channel MOSFET class is the practical next step — many parts from Infineon (OptiMOS), Nexperia, or ON Semiconductor share the same footprint and similar Rds(on) and gate-charge specs, but you will need to verify the gate-drive voltage and switching performance against your actual load conditions.
Gate charge and drive voltage — the logic-level fit
The 20 nC gate charge at 4.5 V and 2200 pF input capacitance at 25 V drain-source are the specs that tell you whether your existing gate-driver can switch this FET fast enough.