In this work CdS thin films were deposited onto glass and p-Si substrates by ultrasonically spraying of precursor solutions prepared in molarity ranging from 0.025 M, to 0.1 M. Structural investigations revealed that all films have hexagonal structure and mean crystallite size was found to be in the range of 18 nm-21 nm. On the other hand, CdS films exhibited 65-70% optical transmittance and band gap energy for all films was found to be about 2.42 eV. Electrical measurements of CdS/Si heterojunctions were carried out under both dark and illumination conditions. Calculated ideality factor and zero-bias barrier height ranged from 3.02 to 2.66 and 0.74 eV-0.78 eV according to TE theory whereas they ranged from 6.91 to 4.73 and 0.71 eV-0.74 eV according to Cheungs' method. Increase in reverse saturation current when heterojunctions were illuminated indicated that they have good sensitivity to solar light.