The condition monitoring of power semiconductor device is significant for the reliability of power electronic system on energy conversion. The ON-state voltage is considered as a critical parameter for power semiconductor device and it’s widely used as an indicator for junction temperature estimation and health monitoring. Hence, this paper proposes a circuit based on depletion MOSFET and its voltage balancing unit extension, which does not require external power supply and can be flexibly extended according to the proposed voltage balancing method to apply to higher voltage applications. The effectiveness of the proposed method is verified by double pulse and AC power cycling tests.