Thin amorphous films of Ge20Sb5S75 composition have been deposited by spin-coating and vacuum thermal evaporation techniques. Their optical properties were investigated by spectroscopic ellipsometry in UV-NIR spectral region. We report on the comparison of thermo- and photo-induced changes in optical parameters, structure and chemical resistance of studied samples. Induced changes of films structure connected with changes of chemical stability were exploited for their surface structuring by photolithography and electron beam lithography. (C) 2017 Elsevier B.V. Ail rights reserved.