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The physical and electrical properties of Ge/GeO 2 /high-gate stacks, where the GeO 2 interlayer is thermally grown in molecular oxygen, are investigated. The high-layer ͑ZrO 2 , HfO 2 , or Al 2 O 3 ͒ is deposited in situ on the GeO 2 interlayer by atomic layer deposition. Detailed analysis of the capacitance-voltage and conductance-frequency characteristics of these devices provides evidence for the efficient passivation of the Ge͑100͒ surface by its thermal oxide layer. A larger flatband voltage hysteresis is observed in HfO 2 -based gate stacks, as compared to Al 2 O 3 gate stacks, which is possibly related to the more pronounced intermixing observed between the HfO 2 and GeO 2 .Inspired by the progress in the development of high-gate dielectrics for Si-based metal-oxide-semiconductor field-effect transistor ͑MOSFET͒ applications, 1 increasing attention is being focused on the feasibility of integrating high-gate dielectrics with germanium ͑Ge͒ because of its intrinsically higher mobility than silicon ͑Si͒. Electrical properties of several high-metal oxides deposited on Ge substrates have been recently reported, including HfO