The heterostructure n-ZnO/p-Si was fabricated by Radio Frequency Sputtering. The photodiode characteristics were obtained from current-voltage curves. The photovoltaic effect and photodiode sensitivity were measured by transient photo-current, both under UV-Light and VIS-Light. The results show a well define rectification character, the relation between current at forward bias and reverse bias was about two orders of magnitude. The photovoltaic effect was observed for UV and Vis light; the photodiode presents a higher sensitivity for Vis light than for UV light. The transient-photocurrent was recorded at a different voltage (-2, -1 and 0 V) under Vis and UV light. The photo-response for UV and Vis light at -1 V were 1.71 mA/W and 9.35 mA/W and for 0 V were 0.62 mA/W and 0.70 mA/W respectively.