Nitrogen was implanted to compensate the negative charges at the interface of the MOS structure and to suppress the coulomb scattering of electrons and also expected to decrease the acceptor concentration at the interface and to make the electric field weak. We have found that the threshold voltage can be controlled by the nitrogen implantation, and the average channel mobility is improved drastically up to 99cm(2)/Vs in 4H-SiC. This result gives a bright to the application of MOS-devices of 4H-SiC. We have found the MOS performance on the C-face can be improved in the same way, although the further optimization of the oxidation condition of the C-face is needed.