To determine the latent degradation of SiC MOSFETs under single-pulse avalanche conditions, the stability of static characteristics and device capacitances is thoroughly studied by conducting Unclamped Inductive Switching (UIS) tests. No parametric shift is observed even though more than 90 % of the maximum avalanche energy is dissipated, indicating that devices fail in an abrupt mode. The avalanche failure turns out to be reaching the critical temperature. By introducing some corrections, including the temperature-dependent material properties, the aluminium layer, and the model of its melting process, the established model provides more accurate temperature results. The derived critical temperature is around 1200 K. All the devices suffer a fusion of metallization, which is considered to be the main mechanism of avalanche failure at the rated current region. With a sufficiently high current, the avalanche failure could also be accelerated by the turning-on of parasitic BJT.