We investigate the Ni–Si film silicidation process on 4H-SiC and Si substrates and compare the thermal stability of the films grown on each substrate. The Ni–Si films were subjected to rapid thermal annealing (RTA) in the temperature range 575 °C–975 °C for 90 s, and their thermal stability was characterized by in-situ temperature-dependent sheet resistance measurements at temperatures of 25 °C–550 °C. The sheet resistance of a 40 nm thick Ni film was observed to increase sharply above 330 °C in the Ni/Si (100) interface, but slightly decrease at approximately 480 °C in the Ni/4H-SiC interface. The thermal stability of the films was found to be significantly dependent on the RTA temperature. Thermally stable Ni–Si silicide films with excellent Ohmic properties (no hysteresis behavior) can be obtained on 4H-SiC substrates at RTA temperatures of 925 °C–975 °C and can used for application in MOSFET devices.