Bandgap radiation in the presence of gaseous oxygen induces surface and selvedge photo-oxidation of amorphous GeS₂. The phenomenon involves preferential oxidation of the Ge sites and may be understood in terms of the structural and electronic properties of GeS₂. Such photo-oxidized films exhibit very different properties towards the subsequent deposition of Ag, as compared with untreated films. The inverse system (GeS₂ deposition on Ag) exhibits markedly different interfacial properties, not previously recognized: this could have significant implications for the interpretation of bulk photodiffusion experiments.