Physical and electrical properties of hafnium-doped tantalum oxide thin films were studied. The doping process affects not only the material properties of the bulk film but also the interface layer's structure and composition. Lightly hafnium- doped tantalum oxide high-k films, i.e., with an equivalent oxide thickness as low as 1.3 nm, have been prepared and studied. The doped film has a bulk layer dielectric constant greater than 28 and an interface layer dielectric constant greater than 8. The film with an EOT of 1.3 nm has a much lower leakage current than that of the SiO2 film with the same thickness. The post-deposition annealing atmosphere showed major impacts on material and electrical properties. The new high-k material is a viable gate dielectric film for future metal-oxide semiconductor transistors.