A single-crystalline ZnGa2O4 epilayer was successfully grown on a c-plane (0001) sapphire substrate through metalorganic chemical vapor deposition. A metal-semiconductor-metal Schottky deep-ultraviolet (DUV) photodetector based on a ZnGa2O4 thin film was fabricated through a simple process of E-gun evaporation and thermal annealing. At a bias of 10 V, the ZnGa2O4 photodetectors exhibited excellent performance characteristics such as an extremely low dark current (0.86 pA), a responsivity of 0.46 A/W under 230-nm DUV, a high photo/dark current ratio (up to 4.68 × 104), a sharp cutoff wavelength of approximately 270 nm, and short rise and fall times of 0.96 and 0.34 s. The photogenerated holes trapped in the Schottky barrier and the shrinking of the depletion region under DUV illumination enabled high DUV/visible rejection ratio (3–4 orders with a 20-V bias). Therefore, the Fowler–Nordheim field tunneling emission functioned as the main electron transport mechanism under DUV illumination and improved the photoelectric characteristics of the epilayer. •High deep-ultraviolet/visible rejection PD based on a ZnGa2O4 epilayer has been fabricated using the Schottky MSM structure.•Dark current for the DUV PD was about 0.86 pA at a bias of ±10 V which was extremely low as compared with those other DUVs.•Under 230-nm DUV (62.5 μW/cm2) illumination, the photocurrent was 4.04 × 10−8 A at a bias of ±10 V.•On/off ratio of the ZnGa2O4 DUV photodetector reached approximately 4–5 orders of magnitude.