Bi₂O₃ thin films were successfully prepared on fluorine doped SnO₂ substrate by the sol–gel route. The effects of annealing temperature on the film structure and photoelectrochemical (PEC) performance were also discussed. Bi₂O₃ thin films were characterized by conventional techniques. X-ray diffraction (XRD) results show the 450 °C annealed film exhibits β-phase structure with the best crystallinity. Scanning electron microscope (SEM) analysis indicates that the surface morphology varies with changing the annealing temperature. The film surface becomes nanoporous at high annealing temperature. Atomic force microscope (AFM) result indicates that the grains on the surface still exhibit close-packed growth in the nanoscale, even though there are many holes in the film surface. The photoelectrochemical performance was evaluated by incident photon-to-current conversion efficiency (IPCE). The IPCE reaches 10.5% at 400 nm (25.5% at 350 nm) without any additional potential vs. Ag/AgCl in 1 M NaOH solution.