Thin films of In0.10Se90 of thickness 200 Å are prepared by vacuum evaporation. The optical gaps (Eoptg) and the high-frequency dielectric constant (ɛɛ∞) are determined from the absorption spectrum of the In0.10Se0.90 films heat-treated at different temperatures. The effect of the temperature of heat treatment on the optical gap (Eoptg) and the high-frequency dielectric constant (ɛɛ∞) of the films is interpreted in terms of the density of state model of Mott and Davis and explained as being due to the saturation of bonds in the amorphous solid. It is shown that in the case of In0.10Se0.90 a transition from the amorphous to the crystalline state takes place at 373 K. The structural analysis of In0.10Se0.90 films by using XRD is reported.