The bonding structure and composition of amorphous silicon suboxide (a-SiO x , 0.25 < x < 0.75) thin films deposited by gas-jet electron beam plasma chemical vapor deposition were studied by Fourier transform infrared (FTIR) spectroscopy, Rutherford backscattering spectroscopy (RBS), and wavelength dispersive X-ray spectroscopy (WDS). Based on the dependence of the integrated absorption of the Si-O-Si asymmetric stretching modes normalized to the silicon atomic density on the x values evaluated by RBS, the proportionality coefficient A SiO of the Si-O-Si asymmetric stretching modes was determined to be 2 × 10 19 cm −2 . Details of the A SiO calculation, the dependence of the silicon atomic density on x, and the limits of integration were discussed. The significant overestimation of the x values obtained from the Si-O-Si stretching mode position in the IR spectra of the films in comparison with the actual values and the presence of a high-frequency shoulder centered at ~ 1140 cm −1 in the IR spectra indicates the inhomogeneity of the structure of the films. At the same time, the parameters of the Si-O-Si asymmetric stretching band (position and full width at half maximum) indicate the absence of a strict phase separation in the structure of the synthesized films, which are thus described by the intermediate model.