In this study, a p-type wide-bandgap oxide semiconductor CuGaO2 thin film was grown on quartz substrate by sol-gel method. The authors report the influence of annealing temperature on the phase transformation, structural features, and electrical properties of sol-gel derived Cu-Ga-O thin films. At relatively low annealing temperatures (<= 900 degrees C), the films are a mixture of CuGa2O4, CuGaO2, and CuO phases. At relatively high annealing temperatures (>= 925 degrees C), the majority phase in the films is delafossite CuGaO2. All as-prepared Cu-Ga-O thin films exhibited p-type conductivity, as confirmed by Hall measurements. The mean electrical resistivity of the Cu-Ga-O films decreased from 3.54x10(4) Omega-cm to 1.35x10(2) Omega-cm and then increased slightly to 3.51x10(2) Omega-cm when the annealing temperature was increased from 850 degrees C to 950 degrees C. We found that annealing the Cu-based oxide thin films at 925 degrees C produced nearly phase-pure CuGaO2 thin films with good densification. Such thin films exhibited the best electrical properties: a mean electrical resistivity of 1.35x10(2) Omega-cm, and a mean hole concentration of 1.60x10(16) cm(-3). In addition, we also fabricated and characterized MSM-type CuGaO2 UV photodetectors on quartz substrates.