In this study, double-layer transparent conductive thin films are formed by depositing silver (Ag) of 99.99% purity on a glass substrate by direct-current (DC) magnetron sputtering, then forming an oxide layer on the Ag layer by depositing gallium-doped indium tin oxide (ITO:Ga) with an ITO:Ga ratio of 97:3 by radio-frequency magnetron sputtering. The films are annealed in vacuum at different temperatures to rearrange the crystals in the films and thereby reduce the defect density. The thicknesses, electrical properties, optical properties, surface structures, and figures of merit (FOMs) of the ITO:Ga/Ag double-layer thin films before and after annealing are analyzed. It is found that the resistivity of the double-layer thin films decreases with increasing annealing temperature and that the lowest resistivity is 5.03×10−5 Ω-cm and the highest average transmittance is 73.33% for the specimen annealed at 450 °C, which also has the highest FOM of 5.31×103 Ω−1. The ITO:Ga/Ag double-layer thin films have excellent optical and electrical properties for photosensor applications.