Ga2O3(Gd2O3), a high kappa gate dielectric, ultrahigh vacuum (UHV)-deposited on GaAs and InGaAs has unpinned the Fermi level in the high-electron-mobility III-V compound semiconductors for the first time. Systematic heat treatments under various gases and temperatures were studied to achieve low leakage currents of 10(-8)-10(-9) A/cm(2) and low interfacial density of states (D-it,(S)) in the range of < 10(11) cm(-2) eV(-1). By removing moisture from the oxide, thermodynamic stability of the Ga2O3(Gd2O3)/GaAs heterostructures and the interfaces were achieved with high temperature annealing, the oxide remains amorphous and the interface remains intact with atomic smoothness and sharpness. The Fermi-level unpinning in atomic layer deposition (ALD) Al2O3 ex-situ deposited on InGaAs was achieved. Recent work of extremely high-quality nano-thick single crystal oxides of gamma-Al2O3 and bixbyite cubic Sc2O3 epitaxially grown on Si(111) is discussed. Interfacial manipulation is essential in giving excellent results presented in the paper. X-ray diffraction, reflectivity, and X-ray photoelectron spectroscopy using synchrotron radiation are critical in probing the interfacial properties. (c) 2006 Elsevier B.V. All rights reserved.