Secondary ion mass spectrometry (SIMS) and electron microscopy have been used to investigate the distribution of hydrogen and chlorine in SiO² films thermally grown on silicon. These films have been grown in various ambients, including pure O², steam, HCl/O², and Cl²/O², as well as HCl/O² mixtures diluted with N². The data suggest that there exists a strong interaction between the chlorine and the hydrogen, with the chlorine being a very effective gettering agent for hydrogen. The results of this investigation, as well as a model explaining the incorporation and distribution of the hydrogen and chlorine, are presented.