By virtue of the carrier avalanche multiplication caused by an impact ionization process occurring in MgO insulation layer, zinc oxide (ZnO)-based ultraviolet (UV) avalanche photodetectors (APDs) have been fabricated from Au/MgO/ZnO/MgO/Au structures. The responsivity of APDs can reach 1.7 × 10 A W , and the avalanche gain of the photodetectors is about 294 at 73 V. Considering that no previous report on ZnO APDs can be found, the results reported in this paper may promise a route to high-performance ZnO UV photodetectors.