Effects of thermal annealing on the interface reactions and the bonding structures of several CeO2/La2O3 stacked dielectrics were studied in detail based on x-ray photoelectron spectroscopy (XPS) measurements. Results indicated that the high-temperature annealing can enhance O, Ce, La, and Si diffusion and result in the intermixing of CeO2/La2O3 stack, growth of interfacial silicates layer at the La2O3/Si interface. A small amount of Ce3+ re-oxidation and significant interface oxidation were found for thermal annealing at 600 degrees C. Based on these observations, reactions taken place at both the CeO2/La2O3 and La2O3/Si interfaces during thermal annealing are proposed. The growth of low-k interfacial layer undoubtedly brings a great challenge for achieving the smallest equivalent oxide thickness (EOT) with superior interface properties. This investigation provides some additional information for possible performance optimization of the high-k gate dielectrics in the subnanometer EOT era. (C) 2016 Elsevier B.V. All rights reserved.