ZnS films were prepared on silicon (Si) and glass substrates by radio-frequency (RF) magnetron sputtering method. The effect of annealing treatment on the structural and optical properties of ZnS films was studied. The results showed that annealing treatment was helpful in improving the crystalline quality of the ZnS films, and the bandgap was about 3.61eV and 3.49eV for films with and without annealing, respectively. A ZnS/ Si heterojunction diode was fabricated successfully by depositing ZnS films on p-type single-crystalline Si substrates. The electrical and optical property of the device was reported.