A high-density vertically well-aligned ZnO nanoneedle array was fabricated on a ZnO-buffer film on silicon substrates by metal-organic chemical vapor deposition at a growth temperature of 480-500 degrees C. Highly crystalline ZnO nanoneedle arrays showed a strong near-bandedge emission at 380 nm in room-temperature photoluminescence. A simple ultraviolet (UV) sensor was fabricated by evaporating a Ag electrode on the ZnO nanoneedle array. The photoresponse results showed very high photocurrent (similar to 10(-4) A) from ZnO nanoneedles compared to a single-nanowire sensor (similar to 10(-8) A), indicating high sensitivity of the photosensor. It also showed fast rise and decay times in UV-on/off switching measurements.