In this paper, the optical characterization of a film of amorphous As-S chalcogenides evaporated on glass substrates will be performed using variable angle of incidence spectroscopic ellipsometry (VASE) and near-normal incidence spectroscopic reflectometry (NNSR), The spectral dependences of the ellipsometric parameters and reflectance of the chalcogenide thin film mentioned is measured within the near-UV, visible and near-IR spectral regions, For interpreting these optical quantities the new dispersion model of the spectral dependences of the optical constants of amorphous solids is employed. This model is based on the modified Lorentz oscillator. Within this model the concepts of the band gap and Urbach tail are respected.