High-k oxides deposited on silicon substrates form interfacial silicon dioxide layers. The interface layer is of importance in microelectronics, due both to charge transport at the silicon/silicon dioxide interface and to the oxide layer influencing the equivalent oxide thickness (EOT). Electrical characterization of low temperature thermal oxides grown by atomic layer deposition of hafnia dioxide indicates a dielectric constant at the interfacial region larger than for stochiometric SiO:. A proposed mechanism for the observed increase is the interface becomes oxygen deficient during the growth process. Oxygen vacancies in SiO2 are examined by ab initio computations and are found to be more stable in the vicinity of the interface, thus identifying a chemical driving force for oxygen reduction at the interface. Copyright The Electrochemical Society.