In summary, an ALT was performed on a ZnGa O photodetector 24with the MSM structure for long-time operation. The ALT results show that ZGO UVC PDs have low reliability, which the dark current and photocurrent vary with the test time, and the response time and rejec- tion ratio also changed a lot after the one-week test. We can observe that the crystallization was almost identical after ALT from the results of SEM and XRD. Incredibly, XPS results show severe water adsorption on the film surface, and the number of oxygen vacancies has also increased due to the degradation of the material after the test. The changes will pro- vide a different leakage path and increase the carrier concentration. The ozone dissociated by mercury lamps compensates the oxygen vacancies and eliminates the response in visible light region. We find out the Al2O3 thin film could form a passivation layer, and the stability of the current level was significantly improved. The rejection ratio was similar after ALT without the influence of the atmosphere. Our results indicate a method to passivate the ZGO UVC PDs with dramatically improve the long time reliability.