In this paper, a new dispersion model of the optical constants of amorphous solids enabling us to perform an efficient parameterization of the spectral dependences of the optical constants of chalcogenide thin films will be presented. This dispersion model is based on mathematical modeling the density of electronic states (DOS) corresponding to both the valence and conduction bands. The imaginary part of the dielectric function is then calculated by the numerical convolution of the DOS. The real part of the dielectric function is calculated using the corresponding Kramers-Kronig (KK) relation in a suitable numerical way. Moreover, the existence of the transitions between the localized states inside the band gap and the extended states inside both the valence and conduction bands is also taken into account using the corresponding convolutions. Thus, the dispersion model presented includes the absorption corresponding to the Urbach and Tauc regions. Then the dispersion model described allows to interpret spectroellipsometric and spectrophotometric data measured for the chalcogenide thin films within the wide spectral region (200-900 nm).