Vertical well-aligned zinc oxide (ZnO) nanowires were grown on p-GaN/sapphire to produce a p-n heterojunction using the vapor-liquid-solid (VLS) process. A p-n heterojunction in an ultraviolet photodetector was successfully demonstrated. The length of ZnO nanowires on the p-GaN epilayer was in the range 0.7-1 mu m and the diameter was in the range 80-100 nm. The current-voltage curve of the heterojunction demonstrates obvious rectifying diode behavior in a dark environment. Under UV light (365 nm), the current was almost 15 times that in the dark current at -5 V. Continuous measurements indicate the reproducibility and stability of this heterojunction photodetector. (C) 2009 Elsevier B.V. All rights reserved.