Abstract: Short circuit protection is critical to ensure that Silicon Carbide (SiC) MOSFET can be safely and reliably turned off under short-circuit fault. Due to SiC MOSFET's short withstand time and no-obvious inflection point of device's drain-source voltage under short-circuit fault, conventional desaturation fault protection (DESAT) circuits for Si IGBT are not applicable for SiC MOSFETs. Therefore, this paper focused on the key parameters for DESAT circuits and developed an appropriate design principles for SiC MOSFETs. This paper further proposed a high-speed, low transmission delay DESAT short circuit protection circuit based on GaN devices. The driving action delay is demonstrated to be 23.2% of the conventional DESAT circuit based on Si devices. Hence, the proposed GaN DESAT circuit is a more superior solution for the SiC MOSFET short circuit protection with lower loss, faster and more compact.