SiC MOSFETs are promising as power switches but suffer from their small drain current. While it is commonly understood that interface defects reduce the number of electrons that contribute to the conduction, the limiting factors of electron mobility is still under debate. In this study, we investigate the impact of bias stress to have an insight about the limiting factors of mobility. Generally, bias stress induces oxide and/or interface defects and hampers the performance of MOSFETs. We investigate the impact of bias stress on the on-state characteristics of SiC MOSFETs. We show how the stress-induced defects affect the device performance and discuss the mobility-limiting factors of MOSFETs.