Infrared transmission spectra of a series of silicon dioxide (SiO2) films grown on silicon wafers from a HCl and O2gas mixture at 850 °C, have been studied for film thicknesses down to 28 A˚. The validity of Lambert‐Bouguer’s Law for such thin films has been confirmed, and the apparent absorption coefficient calculated for the absorption at 1065 cm−1is in good agreement with previously published data for thicker, vapor‐deposited, and thermally grown films. A continuous shift of the absorption near 1065 cm−1has been found, moving from an asymptotic limit maximum of ∼1070 cm−1for thick films towards smaller wave numbers for thinner films. Various possibilities for the origin of this shift are discussed.