This paper deals with online measurement of degradation sensitive electrical parameters leading to a health monitoring approach for power module. The on-state resistance RDSON is a key aging indicator of silicon carbide MOSFETs. It can provide information on both chip and packaging degradation allowing more reliable power electronic converter. This on-state resistance can be determined using both the on-state current and voltage of the power semiconductor. This paper focuses on an on-state voltage measurement circuit for high power modules (up to 3.3 kV, 500A SiC module). A power module switching oscillation model is used to design and fine tune the proposed solution. Finally, the proposed circuit is successfully tested on a double pulse test for various module base plate temperatures and compared to data obtained with a static curve tracer Keysight B1505.