The applicability of secondary ion mass spectrometry (SIMS) was evaluated for measuring the variation of hydrogen distributions in chemical vapor deposition (CVD) SiO2 films by post-oxidation annealing (POA). No noticeable hydrogen migration induced by electron or ion beam irradiation was observed. An increase of hydrogen ion intensity at the thermal SiO2/Si interface was observed regardless of the presence of a CVD SiO2 cap. Also, it was found that POA caused remarkable reduction of the hydrogen concentration at the SiO2/Si interface. This result agreed well with those by grazing incidence X-ray reflectivity (GIXR) and C-V measurements. These results lead us to the conclusion that the excess hydrogen present at the interfacial region was released during re-oxidation. (C) 2004 Elsevier B.V. All rights reserved.