Highly sensitive nanowire switches have been created using ZnO nanowires. The light-induced conductivity increase, which is extremely sensitive to ultraviolet light, allows the reversibly switching of the nanowires between the "OFF" and "ON" states by an optical gating phenomenon analogous to the commonly used electrical gating. The Figure shows a field-emission SEM image of a 60 nm ZnO nanowire bridging four Au electrodes.