Abstract: The effects of post-annealing conducted at 500–650 °C on structural, electrical and optical properties of ZnO film fabricated on GaAs (1 0 0) substrate by atmospheric pressure metal-organic chemical vapor deposition are investigated. X-ray diffraction analyses show that the Zn3As2 and ZnGa2O4 phases are produced for the specimens post-annealed at 500 °C and above. Hall measurements indicate that stable p-type ZnO films with hole concentration ranging from 4.7 × 1018 to 8.7 × 1019 cm−3 can be obtained by modulating the annealing temperature from 500 to 600 °C. In particular, room-temperature photoluminescence (PL) measurements indicate that the superior-quality p-type film could be achieved by a post-annealing treatment at 600 °C. Moreover, low temperature PL spectra at 10 K are dominated by the acceptor-related luminescence mechanisms for the films post-annealed at 550 °C and above. The ionization energy of acceptor was calculated to be 133–146 meV, which is in good agreement with that theoretically predicted for the AsZn–2VZn complex in ZnO. The interdiffused arsenic atoms in the film post-annealed at 600 °C are suggested to form the AsZn–2VZn complex quite effectively, resulting in the most enhanced p-type conductivity and improved material quality.