The porous structure of silicon dioxide layers obtained by chemical vapor deposition during monosilane oxidation by oxygen in the pressure range of 0.5-1.2 Torr at 150 degrees C has been studied by means of adsorption porometry. Mesopore size distribution has been found to be sharply dependent on the pressure of the gas mixture at which the deposition is carried out. The specific surface area of the layers obtained at different pressures has also been measured by means of the adsorption method. It has been stated that over the scale range of about 18-45 Angstrom(2) the surfaces of the layers obtained at 0.5 and 0.8 Torr are fractal. The fractal dimensions of the surface (D) have been determined to be 2.92 +/- 0.10 and 2.78 +/- 0.12, respectively, for the two given pressure values.