The electrical properties and interface reactions of thermally annealed copper (Cu)/4H-SiC (0001) Si-face Schottky rectifiers were investigated in detail by current-voltage characteristics and X-ray photoelectron spectroscopy (XPS). The barrier height of 1.60eV for as-deposited Cu/4H-SiC increased to about 1.80eV after annealing at 500degreesC with keeping the ideality factor below 1.1. The fluctuation of electrical properties under the continuous forward current was not observed for the annealed Schottky rectifiers. However, electrical properties of annealed Cu/4H-SiC over 500degreesC were deteriorated, which is caused by the formation of copper silicides at the Cu/4H-SiC interface.