Spectroscopic ellipsometry and x‐ray diffraction measurements have been used to obtain structural information on hydrogenated amorphous and microcrystalline silicon thin films. The films were deposited onto quartz substrates from a microwave plasma in SiH4/H2gas mixture. For ellipsometric data analysis, the films were modeled as multilayer structures with the dielectric response of each layer calculated as a function of the amorphous, crystallite, and void volume fractions through an effective‐medium approximation. Results indicate that the transition from amorphous‐to‐microcrystalline films is accompanied by a reduction in the material density and a significant increase in the surface roughness overlayer. X‐ray diffraction measurements estimate a higher volume fraction of crystallites as compared to that obtained from optical data.