Silicon carbide (SiC) MOSFETs have been applied in electrical vehicles (EVs) for lower conduction losses and higher efficiency. But long-term reliability issues, especially the stability of gate threshold voltage in switching operation, are crucial. This article investigates the influence of different switching stresses on threshold voltage instability in a boost circuit, and analyses the mechanism of different switching stresses on the degradation of various parts of MOSFETs through capacitance-voltage (C-V) characteristics curves.