Some optical properties of amorphous Ge _xAs _xSe _2-x thin films prepared by thermal "flash" evaporation on the glass substrates at T _substr=100 °C are presented. From transmission spectra T(γ), have been calculated the absorption coefficient α(hν), the values of optical band gap E _g and dispersion curves of refractive index n(γ). It was established that annealing of thin films at high temperatures decreased the absorption coefficient α and refractive index n. The values of optical band gap E _g, determined from the Tauc plot (α-hν) ^1/2 vs. (hν), increased with annealing temperature T _an. Thus, for As _0.09Ge _0.09Se _0.82 composition, the variation of optical band gap versus annealing temperature is ΔE _g/ΔT _an=1.275·10 ^-4 eV/°C. These features may be used in developing of new functional media based on Ge _xAs _xSe _1-2x films for modern optoelectronics.