Cu(In,Ga)Se 2 films were prepared via a sputtering route with a following selenization process. In, CuIn, and Cu 3 Ga were observed in the precursor films. Selenization at 450 o C yielded monophasic Cu(In,Ga)Se 2 films. The diffraction angles of the (112) peaks shifted toward high angles, and a uniform morphology of the obtained films was observed with high-temperature selenization. The amount of gallium ions incorporated into indium ions increased with the temperature. The probable formation mechanism of the sputtering-derived Cu(In,Ga)Se 2 was proposed. Firstly, selenium species diffuse into the precursor films to form Cu(In,Ga)Se 2 and Cu 2−x Se phases. Subsequently, the complete reaction of selenium with residual species leads to the formation reaction of single-phased Cu(In,Ga)Se 2 . An efficiency of 8.34% was achieved for the fabricated solar cell.