Reduction of the net positive charge at the interface between SiO2 and silicon has been achieved by implanting calcium in the SiO2 near the interface and annealing. Comparison between initial calcium implant profiles and calcium profiles obtained after a high-temperature (950 °C) anneal showed that the calcium was basically immobile. A theoretical approach also was employed. Calculations using a model SiO2 structure yielded that among the atomic species examined, calcium was most likely to contribute an effective net negative charge density to the interface when placed randomly at various sites in the model structure.