Structural, optical and electrical properties of CuIn5S8 thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The CuIn5S8 thin films were carried out at substrate temperatures in the temperature range 100-300 degrees C. The effects of heated substrate on their physico-chemical properties were investigated using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), optical transmission and hot probe method. X-ray diffraction revealed that the films are strong preferred orientation along the (3 1 1) plane upon substrate temperature 200 degrees C and amorphous for the substrate temperatures below 200 degrees C. No secondary phases are observed for all the films. The composition is greatly affected by heated substrate. From the optical transmission and reflection, an important absorption coefficient exceeds 10(5) cm(-1) at 800 nm was found. As increasing the substrate temperature, the optical energy band gap decreases from 1.70 eV for the unheated films to 1.25 eV for the deposited films at 300 degrees C. It was found that CuIn5S8 thin film is an n-type semiconductor at 250 degrees C. (C) 2011 Elsevier B.V. All rights reserved.