The electrical characteristics of n-metal oxide semiconductor field effect transistors (n-MOSFETs) fabricated on 4H-SiC with a process based on nitrogen (N) implantation in the channel region before the growth of the gate oxide are reported as a function of the N concentration at the SiO2/SiC interface. A strong correlation among the increase in the N concentration, the reduction of the interface state density near the conduction band and the improvement of the MOSFET performance was obtained. Hall-effect measurements were used to determine the electron mobility and the free carrier concentration in the MOSFET channel. Among the investigated combinations of N dose and oxidation time, the one with the higher dose and the shorter time produces MOSFETs with the higher N concentration at the SiO2/SiC interface and the best electrical characteristics. This superior performance is obtained in spite of the …