Abstract β-Ga₂O₃ epitaxial thin films with different thicknesses were grown on Al₂O₃ (0001) substrates by the pulse laser deposition technology. The full width at half maximum of XRD rocking curve, grain size, surface roughness, and optical absorbance (200–300 nm) of the β-Ga₂O₃ films increase with increasing film thickness. In addition, with increasing film thickness, the adsorption edge presents a red-shift phenomenon, which is accompanied by a slight decrease in the optical band gap ( E g ). The metal-semiconductor-metal type photodetector made with the 401-nm β-Ga₂O₃ film shows the maximal photocurrent (1.06 μA @ 10 V), photo-to-dark current ratio (6.96 × 10⁴), responsivity (90 mA W⁻¹), and detectivity (0.5 × 10¹¹ Jones) under 254-nm UV light illumination with a light intensity of 98.4 μW/cm². Moreover, the 401-nm photodetector displays a small rise time of 0.111/0.561 s and a decay time of 0.046/0.047 s as well as a good stability and repeatability. These findings provide useful reference for the fabrication of β-Ga₂O₃ film based solar blind ultraviolet photodetectors.