Effects of photoirradiation on amorphous As2Se3and As4Se5Ge1thin films are measured in far‐infrared (ir) experiments. Optically enhanced broadenings of the dominant ir absorption bands, similar to that in amorphous Se‐Ge, are described. The broadening degree seems to correspond to an increased randomness in the bond angle of the pyramidal structure. In amorphous As4Se5Ge1, a localized molecular vibration model, consisting of As‐Se and Se‐Ge bonds, is justified.