The ellipsometric study of polycrystalline silicon films deposited using a single wafer rapid thermal chemical vapor deposition reactor under varying conditions of temperature and doping is presented. In particular, using spectroscopic ellipsometry in the visible spectral range, we determined the thickness of the films and the structural changes as a function of the deposition temperature. A different film structure, from amorphous to polycrystalline, has been found for the different deposition temperatures. A shift to lower values of the transition temperature which marks the structural change and a decrease in the deposition rate as the doping level is increased are observed. Moreover, from the ellipsometric results the optical functions of the different samples were evaluated.