This paper investigates the failure modes of SiC MOSFETs-based passive voltage clamping dc solid-state circuit breakers (SSCBs). There are two major concerns of main SiC switch failure that are analyzed in this paper: 1) gate-source voltage ringing related switch degradation/failure when cutting off heavy fault current with high di/dt. 2) thermal runaway directly caused by the short circuit surge current in the main switch before the cut-off and transient power strike during cutoff. Two 10A/86A dc interruption experiments are conducted to demonstrate the failure caused by gate ringing due to the high di/dt issue coupled with unavoidable parasitic common source impedance of the device package. The thermal runaway failure due to the short circuit current surge and transient turn-off power strike is also demonstrated by a 631A dc interruption test. At last, an active commutation current injection scheme is discussed as future research trends to address the revealed gate ringing and cut-off power strike issues in SSCBs.