Samples of a-SiN x :H (0.0≤ x≤0.72) films were obtained by glow discharge decomposition of SiH 4+H 2+NH 3 mixture. The film composition and chemical bonding were determined from infrared absorption data. The bandgap and optical constants (refractive index in the limit of weak absorption and absorption spectra for photon energies higher than bandgap) were obtained from optical transmittance spectra. The density of valence band tail states was deduced from subgap absorption spectra measured by the constant photocurrent method. Raman scattering was measured to estimate the average Si–Si bond deformation potential in a-SiN x :H. Statistical consideration enabled us to compare this value with characteristic energy of tail states distribution. It was established that bond angle disorder in an inhomogeneous structure determined the density of valence band tail states while the approximation of homogeneous alloy with random bonding was not correct.