Dispersion analysis was performed on Fourier transform infrared transmission spectra taken on thermally grown SiO2 films on Si(100) substrates at 950degreesC in dry oxygen with thicknesses between 14 and 100 nm. It was found that within the range 900-1400 cm(-1), these spectra were best described by four Lorentzian oscillators located near 1060, 1089, 1165, and 1220 cm(-1) and within the range 700-900 cm(-1) with two oscillators at 795 and 820 cm(-1), contrary to vitreous silica where the former range is described by two oscillators only and the latter by one. The eventualities that some of these oscillators are due to the existence of oxygen in the Si substrate or to that of SiO2 phases stable at higher temperatures in films were excluded. It was suggested that in thermal SiO2 films the distribution of the Si-O-Si angles is not a simple Gaussian but can be approximated by a superposition of two Gaussians with area ratio of 25/75, distant between them by 6.3degrees and with full widths at half maxima of 13 and 26.8degrees. (C) 2003 The Electrochemical Society.