First-principles calculations of Ge 3d core-level shifts on (100)Ge/Ge(Hf)O-2 interface models, presenting a GeOx transition region that samples different possible oxidation states for Ge atoms near the interface are reported. The fractional densities of these different oxidation states present in the modeled structures are consistent with those inferred from x-ray photoelectron spectroscopy data on thermally oxidized (100)Ge surfaces. The computed relative Ge 3d core-level shifts are in overall fair agreement with the experimental values reported in the literature, especially for the Ge-O-Hf bonds that are likely formed at the GeO2/HfO2 interface. The computed core-level shifts increase linearly with the partial atomic charges on the Ge atoms, consistently with a classical charge-transfer model usually used for the interpretation of experimental data on (100)Ge/Ge(Hf)O-2 interfaces. (c) 2008 American Institute of Physics.