Nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy, and Raman studies on microstructures of hydrogenated silicon films that were fabricated by diluted‐hydrogen and hydrogen‐atom‐treatment methods are presented. The diluted‐hydrogen samples tend to show a very sharp line shape in the NMR spectra at substrate temperatures higher than 300 °C, and the addition of atomic hydrogen treatment can produce the same NMR spectra at a lower temperature of about 250 °C. The Raman scattering spectra show that the atomic hydrogen treatment creates the microcrystalline phase while the diluted‐hydrogen method produces amorphous phase plus a small quantity of microcrystalline phase. The infrared‐absorption spectra also indicate an increase of SiH2 bonding configuration and a hydrogen content reduction when atomic hydrogen treatment is employed. The relation between the origin of the sharp line shape in the NMR spectra and the formation of the microcrystalline phase is also discussed. Together with increase of dark conductivity and reduction of the photo‐to‐dark conductivity ratio, these samples indicate that with appropriate hydrogen incorporation during deposition, and with plasma hydrogen treatment, these films should possess a much more compact structure. These results suggest that the degree of crystallinity of hydrogenated silicon films can be systematically adjusted. A qualitative model based on our experimental data is presented to illustrate the formation procedures of microcrystalline‐phase hydrogenated silicon under the influence of plasma hydrogen and hydrogen dilution.