Uniform p-type CuBi2O4 thin film was prepared through a spin coating method on fluorinedoped tin oxide (FTO) coated glass substrate, with a subsequent hypoxic post-annealing process under semi-sealed condition to enhance its photoelectrochemical efficiency for hydrogen evolution reaction. Compared to CuBi2O4 specimen annealed in open-air environment, the semi-sealed annealed CuBi2O4 photocathode presents a remarkable improvement in cathodic photocurrent, from 0.42 mA/cm(2) to 0.7 mA/cm(2) at 0.25 V-RHE. Xray photoelectron spectroscopy study revealed that the electronic structure of CuBi2O4 film was significantly modified during the post-annealing process and higher carrier concentration was obtained through Mott-Schottky measurement on semi-annealed CuBi2O4. We also demonstrate that the synthesized CuBi2O4 film with a thin overlayer of sputtered TiO2 can retain good stability and efficiency as a photocathode. This work provides insights into the mechanism of the high efficiency CuBi2O4 photocathode achieved from the unique post-annealing treatment. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.