Deposited SiN/SiO2 stack gate structures have been investigated to improve the 4H-SiC MOS interface quality. Capacitance-voltage measurements on fabricated SiN/SiO2 stack gate MIS capacitors have indicated that the interface state density is reduced by post-deposition annealing in N2O at 1300°C. The usage of thin SiN and increase in N2O-annealing time lead to a low interface state density of 1×1011 cm-2eV-1 at EC – 0.2 eV. Oxidation of the SiN during N2O annealing has resulted in improvement of SiC MIS interface. The fabricated SiN/SiO2 stack gate MISFETs demonstrate a high channel mobility of 32 cm2/Vs on (0001)Si face and 40 cm2/Vs on (000-1)C face.