This paper describes reliability experiments on 1200 V SiC power n-MOSFETs manufactured by three different manufacturers utilizing two different mechanisms: accelerated thermal aging and bias temperature instability. Each of the devices was electrically tested for evaluating variation of pre- and post-stress I–V characteristics. Pre-stress evaluation of threshold voltage (V_th) for 25 cycles showed transient behavior and a saturation toward an average value. For thermal aging reliability test, devices were stressed at 120 °C for 200 h and 3.33% of the devices showed significant shift in threshold voltage (V_th). For bias temperature instability measurement, devices were stressed at 120 °C for 200 h and a bias voltage of 20 V was applied across the gate–source terminals. For 96.7% device, V_th demonstrated an increment with stressing time and a movement toward saturation.