In this paper, we consider ToF-SIMS as a tool to monitor interfacial SiO2 at high-k/Si interfaces. By comparing TEM with ToF-SIMS profiles, a correlation between interfacial SiO2 formation and SiO2- signal is drawn, leading to a methodology to measure interfacial SiO2 layer thickness by means of ToF-SIMS. A strong preferential sputtering of oxygen in the high-k layer is observed, and this affects the possibility to determine interfacial SiO2 layer thickness with ToF-SIMS. Interfacial effects occurring at the high-k/SiO2/interface are discussed, and a simple qualitative model for the sputtering process at the interface is presented. (C) 2004 Elsevier B.V. All rights reserved.