ZnO nanowires (NWs) were fabricated on p-Si (100) substrates by simple physical vapor deposition in vacuum furnace. Scanning electron microscopy (SEM) images indicate that the diameters of ZnO NWs were from 20 to 50 nm and the average length was longer than 2 μm. Room-temperature photoluminescence spectra of the NWs show the near bandedge emissions and the deep-level green light emissions. Such result indicates that the nanowires have good structural quality. We have fabricated electrical biosensors based on ZnO NW field effect transistors and report the chemical sensitivity of ZnO NWs. The ZnO nanosensor functionalized with biotin can easily detect streptavidin binding. The ZnO NWs for sensitive, label-free, real time detection of a wide range of biological species could be exploited in vivo diagnostics.