The interfacial and electrical properties of Ge-based metal-oxide-semiconductor (MOS) capacitor with high-k gate dielectric of HfTiO and passivation interlayer of LaTaON are investigated. Experimental results show the Ge MOS with HfTiO/LaTaON gate-stacked dielectric exhibits low interfacestate density (7.8 × 10 11 cm −2 eV −1 ), small gate-leakage current (7.88 × 10 −4 A cm −2 at V g − V fb = 1 V), small capacitance equivalent thickness (1.1 nm), and large equivalent dielectric constant (27.7). X-ray photoelectron spectroscopy and transmission electron microscopy reveal that the improvements should be due to the fact that La/Ta-based oxide/oxynitride has excellent interface properties with Ge, and the LaTaON interlayer can effectively block the in-diffusion of oxygen and the out-diffusion of germanium, thus suppressing the growth of low-k GeO x and intermixing between Ge and Hf.Index Terms-Ge metal-oxide-semiconductor (Ge MOS), high-k dielectric, interface properties, LaTaON, passivation layer.