Selenium doped with arsenic thin films prepared by thermal evaporation were exposed to white light in air. The structure of thin films gradually changed from amorphous to polycrystalline as the time of exposure and film temperature increased. The grain size increases up to 27.69 nm when the As doped Se thin film was exposed to light for 1 h. The electrical resistivity behaviour as a function of temperature and exposure time was detected for films deposited on glass and mica substrates. The activation energies were calculated in darkness and during illumination for deposited materials. The refractive index (n) and absorption coefficient (alpha) were determined before and after phototransformation.