CuGaS2 thin film is fabricated with electrochemical deposition of Cu-Ga alloys from alcohol solution to eliminate the interference of hydrogen evolution reaction (HER). The process involves electrodeposition of Cu-Ga precursor on molybdenum substrate and subsequential annealing in sulfur vapor. The formation of CuGa2 alloy in precursor is observed and pure ternary chalcopyrite CuGaS2 phase in good polycrystalline structure without secondary phase is obtained after thermal treatment. The influence of the applied deposition potential on the crystalline phase, morphology, compositions, and carrier concentration of the films were investigated. The results show that an optimum choice of electrodeposition potential is necessary to obtain a pure crystallized CuGaS2 thin film. A lower absolute deposition potential results in a higher Cu/Ga ratio and the emergence of CuS secondary phase after annealing in sulfur atmosphere. The crystal size of the formed CuGaS2 phase with thermal annealing process increases with the positive shift of deposition potential. Impedance spectroscopy test demonstrates the semiconductor property of the synthesized CuGaS2 polycrystalline thin films are all p-type. The carrier density of the obtained CuGaS2 thin films increases with the negative shift of deposited potential.