In this study, CdS films prepared using the technique of pyrolysis spray at the glass and Si wafer with a thickness of 300 nm using Cadmium Acetate Cd (CH3COO)2·2H2O with purity of 99.6% and Thiourea (CS(NH2)2) with purity 99.6%. These compounds are used as the sourced materials of Cd+2 and S-2 ions, respectively for the CdS films formation. The films were annealed at different temperatures (400, 500, and 600 0C), then the effect of annealing on its properties was studied. The high-quality films were obtained as evident using XRD analysis. X-ray diffraction analysis for all CdS films was polycrystalline with cubic and hexagonal wurtzite structure with preferential orientation in the H (002) and C (111) direction. It is difficult to distinguish between them, after high-temperature process from 400 0C to 6000C, new peaks of the hexagonal structure appeared. This phenomenon was thought to be the phase change of CdS thin film by heat treatment as well as the increasing of intensity of H (002) and decreases in full width at half maxima (FWHM) the grains size with annealing. The CdS photodetector and the spectral response of CdS/Si junction was studied. The maximum value of responsivity occurred at a wavelength of 500 nm to 560 nm. The maximum values of D* and η at Ta equal to 500 0C. Whereas, they increase and shift to higher wavelength with the increase of Ta. It has been observed that the best spectral response occurs when the annealing temperature equal to 500 0C, therefore, is essential to say that this value of Ta was the optimum condition for prepared CdS photoconductive detector.