Negative ionization probability in SIMS has been the subject of several investigations, with special emphasis on the effect of alkali metals adsorption. Those studies are aimed to correlate non-local surface properties (i.e. work function) to the ionization probability. In theory on insulators non-local effects cannot explain the ionization probability since the ionization process is thought to be governed by local effects. In this paper, we study the ionization probability in silicon and in silicon oxide as a function of non-local effects both in silicon and in silicon oxide, by sputtering with cesium at different fluences with a dual beam ToF-SIMS. We introduce the concept of total ionization probability measured as the total fraction of a certain element that is detectable with SIMS. We observe that such a parameter is constant for silicon in a SiO2/Si system. We exploit this feature to perform quantitative depth profiling at interfaces SiO2/Si on oxynitrides and SiO2/Si3N4/SiO2 stacked structures. (C) 2002 Elsevier Science B.V. All rights reserved.