Re: power mosfet(req)
One important characteristic of power MOSFET is Rdson - ON resistance (when transistor is opened). Rdson includes two components - channel resistance,
and parasitic series source-drain resistance due to metal interconnects structure (this structure may include several layers of metallization and quite complicated layouts, to supply source and drain connections to a very large area array of transistors).
Parasitic resistance depends on number of metal layers, metal layouts, metal thicknesses, bond wire placement, etc.
Among other important characteristics are parasitic capacitances (gate to source and drain), parasitic inductance (source), gate charge, etc.