Abstract Optical absorption measurements have been made on thin films, 0.3–0.5 μm thick of amorphous Ga 40Se x Te 60 - x alloys 20 < x < 40 prepared by vacuum evaporation. These measurements have been made on the as-prepared and annealed samples. It was observed that annealing affects the optical properties and causes a reduction in the energy range of tail states. The optical energy gap in all the alloys increases. The mechanism of optical absorption follows the rule of non-direct transitions. The results obtained for different samples are compared with each other. Like the activation energy of dc conductivity, the optical band gap before and after annealing increases with the amount of Se in these alloys.