Au/Ni/n-type 4H–SiC Schottky alpha particle detectors are fabricated and annealed at temperatures between 400 ℃ and 700 ℃ to investigate the effects of thermal stability of the Schottky contact on the structural and electrical properties of the detectors. At the annealing temperature of 500 ℃, the two nickel silicides (i.e., Ni31Si12 and Ni2Si) are formed at the interface and result in the formation of an inhomogeneous Schottky barrier. By increasing the annealing temperature, the Ni31Si12 transforms into the more stable Ni2Si. The structural evolution of the Schottky contact directly affects the electrical properties and alpha particle energy resolutions of the detectors. A better energy resolution of 2.60％is obtained for 5.48-MeV alpha particles with the detector after being annealed at 600 ℃. As a result, the Au/Ni/n-type 4H–SiC Schottky detector shows a good performance after thermal treatment at temperatures up to 700℃.