An ambient composed of hydrogen (≥ 95%), carbon dioxide (0.5–5%), and silicon tetrabromide (0.1–1%) will deposit a film of silica on a substrate heated to 800°–850°C. The process has particular application for coating germanium for high‐speed planar device technology; it is useful for silicon also. The reaction may be carried out immediately after epitaxial germanium deposition in the same equipment.Silica growth rates are of the order of 100 Aå/min; rates for various temperatures and concentrations are presented. Apparent activation energy is 30 kcal/mole. The oxide films are clear, vitreous, and adherent, with no detectable structure. Electrical properties of MOS diodes made on silicon are comparable to, or superior to, conventional steam‐grown oxide. The film is a satisfactory mask against 1200° boron diffusion. The silica contains about 2% residual bromine, apparently in a form in which it is not free to migrate.