Gallium oxide (Ga 2 O 3 ) thin films were deposited on a-Al 2 O 3 (11 20) substrates by pulsed laser deposition (PLD) with different oxygen pressures at 650 • C. By reducing the oxygen pressure, mixed-phase Ga 2 O 3 films with α and β phases can be obtained, and on the basis of this, mixed-phase Ga 2 O 3 thin film solar-blind photodetectors (SBPDs) were prepared. Comparing the responsivities of the mixed-phase Ga 2 O 3 SBPDs and the single β -Ga 2 O 3 SBPDs at a bias voltage of 25 V, it is found that the former has a maximum responsivity of approximately 12 A/W, which is approximately two orders of magnitude larger than that of the latter. This result shows that the mixed-phase structure of Ga 2 O 3 thin films can be used to prepare high-responsivity SBPDs. Moreover, the cause of this phenomenon was investigated, which will provide a feasible way to improve the responsivity of Ga 2 O 3 thin film SBPDs.