In this letter, we describe a process for the preparation of high-quality tantalum oxynitride (TaOxNy) with zirconium silicate (ZrSixOy) as an interfacial layer for use in gate dielectric applications. Compared with conventional chemical oxide and nitride as interfacial layers, TaOxNy metal–oxide–semiconductor capacitors using ZrSixOy as an interfacial layer exhibit lower leakage current levels at the same oxide thickness and a lower interface state density. We were able to confirm the TaOxNy/ZrSixOy stack structure by Auger electron spectroscopy and transmission electron microscopy analyses. Zirconium silicate is a promising interfacial layer for future high-k gate dielectric applications. © 2001 American Institute of Physics.