We investigate the effects of NO annealing and forming gas(FG) annealing on the electrical properties of a SiO_2/SiC interface by low-temperature conductance measurements.With nitrogen passivation,the density of interface states(D_(IT)) is significantly reduced in the entire energy range,and the shift of flatband voltage,△V_(FB),is effectively suppressed to less than 0.4 V.However,very fast states are observed after NO annealing and the response frequencies are higherthan 1 MHz at room temperature.After additional FG annealing,the D_(IT) and △V_(FB) are further reduced.The values of the D_(IT) decrease to less than 10~(11) cm~(-2) eV~(-1) for the energy range of E_C-E_T≥0.4 eV.It is suggested that the fast states in shallow energy levels originated from the N atoms accumulating at the interface by NO annealing.Though FG annealing has a limited effect on these shallow traps,hydrogen can terminate the residual Si and C dangling bonds corresponding to traps at deep energy levels and improve the interface quality further.It is indicated that NO annealing in conjunction with FG annealing will be a better post-oxidation process method for high performance SiC MOSFETs. We investigate the effects of NO annealing and forming gas (FG) annealing on the electrical properties of a SiO 2 / SiC interface by low-temperature conductance measurements. Whith nitrogen passivation, the density of interface states (D_ (IT)) is significantly reduced in the entire energy range, and the shift of the flatband voltage, ΔV_ (FB), is effectively suppressed to less than 0.4 V. Even, very fast states are observed after NO annealing and the response frequencies are higherthan 1 MHz at room temperature. After additional FG annealing, the D_ (IT) and ΔV_ (FB) are further reduced. The values ​​of the D_ (IT) decrease to less than 10 ~ (11) cm -2 eV -1 for the energy range of E_C-E_T ≥ 0.4 eV.It is suggested that the fast states in shallow energy levels originated from the N atoms accumulating at the interface by NO annealing. Hough FG annealing has a limited effect on these shallow traps, hydrogen can terminate the residual Si and C dangling bonds corresponding to traps at deep energy levels and improve the interface quality further. It is indicated that NO annealing in conjunction with FG annealing will be a better post-oxidation process method for high performance SiC MOSFETs.