In this work, the degradation mechanism of 1.2kV 4H-SiC MOSFET under repetitive Unclamped Inductive Switching (UIS) stress has been investigated. The hot-holes injection and trapping into the gate oxide above the JFET region is observed, resulting in the increase of the off-state drain-source leakage current (I DSS ) and the decrease of the on-state resistance (R dson ). Moreover, an improved device with step gate oxide above the JFET region is proposed, which can effectively restrict the degradation under repetitive UIS stress, while the fresh breakdown voltage (BV) and R dson are almost unaffected.