SiC metal-oxide-semiconductor field effect transistor (MOSFET) with n-layer channel structure is fabricated and characterized. Influence of depletion region length on specific on-resistance is investigated from calculation and experiment. Depletion region length over 5 mum or doping of drift layer over 5 x 10(15)/cm(3) are required for depletion region resistance below 10 mOmegacm(2) from the calculation. The evaluated values are coincident with the values measured from fabricated SiC MOSFETs; epilayer channel MOSFET and channel doped MOSFET.