In this payer the method based on interpreting the data measured within variable angle of incidence spectroscopic ellipsometry and spectroscopic reflectometry is used for the complete optical analysis of hydrogenated amorphous silicon layers deposited on silicon single crystal wafers. This method enables us to perform the analysis of these layers in a relatively wide spectral region because a new model of dispersion of the optical constants of the hydrogenated amorphous silicon layers was constructed. Moreover, the influences of both roughness and native oxide layer existing on the upper boundary of every silicon layer studied is respected at its analysis. The results obtained for a chosen sample of the hydrogenated amorphous silicon layer are presented.