Thin films ofa‐Ge:H with hydrogen contents ranging from 0 to 13 at. % prepared by the glow‐discharge process have been studied by spectroscopic ellipsometry. The resulting ellipsometric parameters have been analyzed by using standardn‐layer models, least‐squares regression analysis, and the Bruggeman effective media approximation theory. The results of the analyses show that the atomic percentage of hydrogen, in the amorphous binary alloy of Ge and H, can be represented by a void volume fraction in an effective medium approximation. These results are compared with those of infrared absorption spectroscopy. A good correlation between the percentage void determined from ellipsometry and the H content measured in thesea‐Ge:H films is found.