This investigation demonstrates the effect of high-pressure H2O treatment on the elimination of the interfacial germanium suboxide (GeO X) layer between ZrO2 and Ge. The formation of GeO X interlayer increases the gate-leakage current and worsen the controllability of the gate during deposition or thermal cycles. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy reveal that high-pressure H2O treatment eliminates the interfacial GeOX layer. The physical mechanism involves the oxidation of non-oxidized Zr with H2O and the reduction of GeOX by H2. Treatment with H2O reduces the gate-leakage current of a ZrO2/Ge capacitor by a factor of 1000.