The Ag/n-ZnO/p-Si(100)/Al heterojunction diodes are fabricated by pulsed laser deposition of ZnO thin films are on p-Si. High purity vacuum evaporated silver and aluminum metals were used to make contacts to the n-ZnO and p-Si, respectively. The current–voltage characteristics of Ag/n-ZnO/p-Si(100)/Al structure measured over the temperature range 80-300K have been studied on the basis of thermionic emission diffusion mechanism. The Schottky barrier height and diodes ideality factor are determined by fitting of measured current–voltage data in to thermionic diffusion equation. It is observed that the barrier height decreases and the ideality factor increases with decrease of temperature and the activation energy plot exhibit non-linear behavior. This decrease in barrier height and increase in ideality factor at low temperature are attributed to the occurrence Gaussian distribution of barrier heights. The capacitance–voltage characteristics of Ag/n-ZnO/p-Si(100)/Al heterojunction diode are also studied over the wide temperature range.