High speed switching circuits using SiC power device have been developed for downsizing of electric products. The high speed switching leads to the rapid changing of the drain voltage (dV/dt). This paper reports the effects of the dV/dt impact on the self-turn-on and the characteristics of SiC-MOSFET. The results shows that the gate bias voltage to suppress the self-turn-on is negatively correlated with the temperature. And it is also found that the dV/dt impact breaks down the gate source insulation and the dV/dt value to the breakdown is positively correlated with the temperature.