Abstract: The gate oxide degradation has become a crucial factor restricting the reliability of SiC metal oxide semiconductor field effect transistor (MOSFET). This paper attempts to obtain gate oxide state information by using the high-frequency (HF) switching oscillations caused by SiC MOSFETs high-speed switching in converters. The effect of gate oxide degradation on SiC MOSFETs gate turn-on oscillation is explored. First, the aging mechanism of SiC MOSFETs gate oxide and its influence on device turn-on time are analyzed. Then, a multi-stages HF equivalent model of gate loop during turn-on transient is established to reveal the formation mechanism and dominating factors of gate turn-on oscillation. Finally, a 33 V high voltage gate bias accelerated aging experiment is conducted for verification. The research results show that the threshold voltage of SiC MOSFETs increases and the turn-on speed becomes slower with the development of gate oxide aging. Consequently, a significant reduction of about 28% is observed in the gate turn-on oscillation current. The presented work is expected to provide a new idea for online monitoring of SiC MOSFETs gate oxide aging.