The electrical characteristics of MOSFETs fabricated on 4H-SiC with a process based on 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 up to 6 1019 cm-3. The field effect mobility improves with increasing N concentration. At room temperature values change from 4 cm2/Vs for the not implanted sample up to 42 cm2/Vs for the sample with the highest N concentration. Furthermore, the field effect mobility increases with temperature and presents values above 60 cm2/Vs at 200 °C. The MOSFETs with the better electrical characteristics (higher mobility, lower threshold voltage, lower subthreshold swing) were fabricated by a low thermal budget oxidation process, thank to the use of a high N implantation dose able to produce an amorphous SiC surface layer. A strong correlation among the increasing of the N concentration at the SiO2/SiC interface, the reduction of the interface state density located near the conduction band and the improvement of the MOSFETs performance was obtained.