Method of testing semiconductor device

A first relational expression for a temperature of a semiconductor device and forward voltage of a temperature measurement diode is obtained in advance. A second relational expression is obtained in advance for ON voltage of the semiconductor device and an amount of temperature change from a first time point before ON of the semiconductor device until a second time point after OFF of the semiconductor device. An amount of forward voltage change of the temperature measurement diode from the first time point until the second time point is obtained. Next, the amount of temperature change from the first time point until the time second point is calculated using the first relational expression and the amount of forward voltage change. An ON voltage of the MOS gate semiconductor device after correction for the calculated amount of temperature change is obtained using the second relational expression.