Silicon carbide (SiC) MOSFETs has been applied in electrical vehicle (EV) for lower conduction losses and higher efficiency. But long-term reliability issue especially, the stability of gate threshold voltage in switching operation is crucial. This article investigates the influence of different switching stress on threshold voltage instability in a boost circuit, and analyses mechanism of different switching stress on the degradation of various parts of MOSFETs through capacitance-voltage (C-V) characteristics curve.