N-ZnO/p-Si heterojunctions are prepared by sputtering deposition of intrinsic ZnO films on p-Si substrates.Thicknesses of ZnO films are altered by varying the deposition time from I h to 3 h.The electrical properties of these structures are analysed from capacitance-voltage ( C- V) and current-voltage (I- V) characteristics performed in a dark room.The results demonstrated that all the samples show strong rectifying behaviour.Photovoltalc property for the samples with different thicknesses of ZnO films are investigated by measuring open circuit voltage and short circuit current.It is found that photovoltages are kept to be almost constant of 32OmV along with the thickness while photocurrents changing a lot.The variation mechanism of the photovoltalc effect as a function of thickness of ZnO films is investigated.