The condition monitoring of high power IGBT module is significant for the reliability of power electronic equipment. The ON-state voltage is considered as a critical parameter for IGBTs and it’s widely used as an indicator for junction temperature estimation and health monitoring. However, the high amplitude jump of the device voltage in the high-voltage module brings new challenges to the on-state voltage measurement. This paper proposes a series circuit based on depletion MOSFET for ON-state voltage extraction and junction temperature monitoring of high voltage and high power IGBT module. The experimental results show that the proposed circuit has great expandability and the error is less than 6mV, which proves the accuracy of proposed method.