The effect of rapid thermal annealing temperature on the structural and electrical properties thin ZnO films grown on GaAs substrate by atomic layer deposition is thoroughly investigated. X-ray diffraction analysis show that atoms interdiffusion can be observed at the interface of ZnO/GaAs heterostructures after annealing in oxygen ambience at elevated temperatures. Moreover, the conductivity of ZnO film converts from n- to p-type after annealing at 600 °C. A hole concentration as high as 3.4 × 10 20 cm −3 is also obtained for the sample annealed at 650 °C. The p-type conductivity of ZnO films is attributed to arsenic atoms diffusion into ZnO films as shallow acceptors.