In this work, we present experimental results examining the energy distribution of the relatively high (> 1 X 10(11) cm(-2)) electrically active interface defects which are commonly observed in high-dielectric-constant (high-k) metal-insulator-silicon systems during high-k process development. This paper extends previous studies on the Si(100)/SiOx/HfO2 system to include a comparative analysis of the density and energy distribution of interface defects for HfO2, lanthanum silicate (LaSiOx), and Gd2O3 thin films on (100) orientation silicon formed by a range of deposition techniques. The analysis of the interface defect density across the energy gap, for samples which experience no H-2/N-2 annealing following the gate stack formation, reveals a peak density (similar to 2 X 10(12) cm(-2) eV(-1) to similar to 1 X 10(13) cm(-2) eV(-1)) at 0.83-0.92 eV above the silicon valence bandedge for the HfO2, LaSiOx, and Gd2O3 thin films on Si (100). The characteristic peak in the interface state density (0.83-0.92 eV) is obtained for samples where no interface silicon oxide layer is observed from transmission electron microscopy. Analysis suggests silicon dangling bond (P-bo) centers as the common origin for the dominant interface defects for the various Si(100)/SiOx/high-k/metal gate systems. The results of forming gas (H-2/N-2) annealing over the temperature range 350-555 degrees C are presented and indicate interface state density reduction, as expected for silicon dangling bond centers. The technological relevance of the results is discussed. (c) 2007 The Electrochemical Society.