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In this study, 60-nm-thick Ga2O3 films were deposited on c-plane sapphire substrates by atomic layer deposition process. The effect of annealing temperature on both Ga2O3 material and optical response characteristics was studied by ultraviolet–visible spectroscopy, X-ray diffraction and semiconductor parameter analyzer. When the annealing temperature exceeds 700 ℃, the Ga2O3 films exhibits a nanocrystalline β-phase. The Ga2O3 photoconductive solar-blind photodetectors annealed at different temperature were fabricated. The photo-current and responsivity first increase slowly and then decrease when the annealing temperature changes from 400 to 1000 ℃. An ultra-high photoresponsivity of 142 A/W with detectivity of 3.77 × 1015 Jones under 254 nm illumination was achieved for the Ga2O3 film annealed at 600 ℃ for 60 min in N2/Air mixture atmosphere, which is at a very high level for ultraviolet photodetectors based on Ga2O3 thin films (< 100 nm). When the annealing temperature is 600 ℃, the material is in the transition stage from amorphous to crystalline state, which leads to a high degree of disorder, and further results in obvious band-tail absorption effect and improves the photoresponsivity. The results provide important guidance for the preparation of solar-blind ultraviolet detectors with ultra-high performance. [ABSTRACT FROM AUTHOR]