In this paper the results of the study of the optical properties of diamond-like carbon films with different amount of SiOx prepared by plasma enhanced chemical vapor deposition from a mixture of methane and hexamethyldisiloxane onto silicon substrates will be presented. These results have been obtained using the combined method based on a simultaneous interpretation of experimental data achieved with variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry within the near-UV and visible regions. For interpreting the experimental data our new dispersion model of the optical constants based on the parameterization of the density of electronic states has been employed. Within this model the new analytical three parameter dispersion formula has been derived. These three parameters are proportional to the pi and sigma valence electron densities. (C) 2003 Elsevier B.V. All rights reserved.