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An experimental examination of the properties of the Si(100)–SiO2 interface measured following rapid thermal processing (RTP) is presented. The interface properties have been examined using high frequency and quasi-static capacitance-voltage (CV) analysis of metal-oxide-silicon (MOS) capacitor structures immediately following either rapid thermal oxidation (RTO) or rapid thermal annealing (RTA). The experimental results reveal a characteristic peak in the CV response measured following dry RTO and RTA (T>800 °C), as the Fermi level at the Si(100)–SiO2 interface approaches the conduction band edge. Analysis of the QSCV responses reveals a high interface state density across the energy gap following dry RTO and RTA processing, with a characteristic peak density in the range 5.5×1012 to 1.7×1013 cm−2 eV−1 located at approximately 0.85–0.88 eV above the valence band edge. When the background density of states for a hydrogen-passivated interface is subtracted, another peak of lower density (3×1012 to 7×1012 cm−2 eV−1) is observed at approximately 0.25–0.33 eV above the valence band edge. The experimental results point to a common interface state defect present after processes involving rapid cooling (101–102 °C/s) from a temperature of 800 °C or above, in a hydrogen free ambient. This work demonstrates that the interface states measured following RTP (T>800 °C) are the net contribution of the Pb0/Pb1 silicon dangling bond defects for the oxidized Si(100) orientation. An important conclusion arising from this work is that the primary effect of an RTA in nitrogen (600–1050 °C) is to cause hydrogen desorption from pre-existing Pb0/Pb1 silicon dangling bond defects. The implications of this work to the study of the Si–SiO2 interface, and the technological implications for silicon based MOS processes, are briefly discussed. The significance of these new results to thin oxide growth and optimization by RTO are also considered.