Doping-dependent fixed charges, which are not observed in Si MOSFETs, were found in SiC MOSFETs through the study on the relationship between threshold voltage and body doping. As body-doping density increases, positive fixed charges increase for p-body (n-channel) devices and negative fixed charges increase for n-body (p-channel) devices. It is suggested that the generation of the fixed charges is related to the Fermi level at a final treatment (NO annealing) temperature. These fixed charges cause a threshold voltage lowering from the theoretical value, especially in heavily-doped MOSFETs. Thus, the Fermi level at a final treatment temperature should be considered to precisely control threshold voltage in SiC MOSFETs.