In this work, Ga doped ZnO (GZO)/CdS bilayer films were prepared on p-Si substrate by magnetron sputtering to form GZO/CdS/p-Si heterojunction device. The structural, optical and electrical properies of the nanocrystalline GZO/CdS bilayer films were studied by XRD, SEM, XPS, UV-VIS spectrophotometer and Hall effect measurement. The J-V curve of GZO/CdS/p-Si heterojunction device shows good rectifying behavior. And the value of IF/IR (IF and IR stand for forward and reverse current, respectively) at ±3V is found to be as high as 21. The results indicate that the nanocrystalline GZO/CdS/p-Si heterojunction possesses good diode characteristic. High photocurrent density is obtained under a reverse bias. The nanocrystalline GZO/CdS/p-Si heterojunction device exhibits clear photovoltaic effect. Because the lattice constant of CdS is between GZO and Si, it can be used for a buffer layer between GZO and Si, to effectively reduce the interface states between GZO and p-Si. Therefore, we observed the clear photovoltaic effect of GZO/CdS/p-Si heterojunction.