Dielectric constant and dissipation factor at 1 kHz for films formed by vacuum evaporation of silicon monoxide have been measured as a function of deposition rate and residual oxygen pressure. The dielectric properties are found to depend strongly on the ratio of molecular‐impingement rates at the substrate of O2and SiO. A model based on changes in the film of the concentrations of Si, SiO, and Si2O3is proposed to explain the dielectric behavior. The model is compared to optical data reported by other workers.