Abstract The electrical performance of silicon carbide metal-oxide-semiconductor field effect transistors (4H-SiC MOSFETs) are strongly related to the presence of interface states at the silicon dioxide (SiO 2 )/4H-SiC interface, whose density is much higher than in the Si/SiO 2 system. In particular, the charged interface states determine a degradation of the carrier mobility in the channel of the MOSFET with respect to the bulk mobility. A reliable and consistent method for the evaluation of the interface state density ( D it ) and the effective channel mobility ( μ ch ) in these devices is presented in this work. The two quantities are simultaneously extracted by a combined fit of the current–voltage ( I – V ) and capacitance–voltage ( C – V ) electrical characteristics collected on a single device. The simultaneous fit of the I – V and C – V characteristics, which can be easily measured on the same device, noticeably improve the reliability of D it and μ ch estimation. The results obtained at different temperatures indicate an increase of the μ ch with T , in agreement with a dominance of the Coulomb scattering effect as the degradation mechanism of the carrier channel mobility induced by the presence of charged interface states.