This study shows that visible light ellipsometry can be used to measure the thickness of polycrystalline silicon films that have been deposited on oxidized Si slices. The measurement hinges on obtaining a value for the complex index of refraction, Ñ, for the polycrystalline silicon films. An empirical method has been found which gives usable values for Ñ. The limits of application of the ellipsometric technique are shown. Also, it is shown that discontinuous polycrystalline silicon films can be detected using ellipsometry. Finally, although theoretically possible, the accurate measurement of oxide grown on polycrystalline silicon surfaces is not practical. © 1982, The Electrochemical Society, Inc. All rights reserved.