The aim of this study is to understand the structural, optical and photo-electrical properties of the quaternary chalcogenide AgGa0.5In0.5Te2 thin films deposited onto the glass substrates by thermal evaporation of the single crystalline powder. Energy dispersive X-ray analysis (EDXA) showed remarkable change in atomic percentage of the constituent elements after annealing. The X-ray diffraction (XRD) of the films below the annealing temperature of 300 degrees C indicated the polycrystalline structure with co-existence of AgGaTe2 and AgGa0.5In0.5Te2 phases. However, the single phase of AgGa0.5In0.5Te2 chalcopyrite structure was obtained at the annealing of 300 degrees C. The band gap values were calculated in between 1.05 and 1.37 eV depending on annealing temperature. The temperature dependent photoconductivity was measured under different illumination intensity. The nature of existing trap levels were studied by measuring the variation of photocurrent as a function of illumination intensity. The analysis showed that AgGa0.5In0.5Te2 thin film changes its behavior from the sublinear to supralinear photoconductivity after annealing. (C) 2010 Elsevier B.V. All rights reserved.