Illumination of amorphous As2S3 film by ultraviolet light with an overall light intensity on the sample surface of around 10 Wcm- 2 leads to extensive film oxidation. After two minutes of illumination most of As2S3 film of an original thickness at around 0.425 μm was converted into a cubic form of As2O3 – arsenolite. A considerable amount of arsenolite microcrystals were found at a height of around 2 μm and more which indicated a growth of As2O3 microcrystalline particles from the vapor phase.