The formation of Gd2O3/substrate-GaAs structure was accomplished by two-step electron-beam (e-beam) deposition including ultra-thin Gd-metal and successive Gd2O3 layers. The deposition was carried out on HCl-cleaned GaAs containing elemental As on it. The pre-deposition of Gd-metal removes elemental As state in GaAs surface and forms interfacial state free from GaAs-oxides. However, Gd-metal turns to be oxide during the deposition by absorbing oxygen from GaAs surface and atmosphere. The successive deposition of Gd2O3 was performed with in situ anneal of the substrate and this permitted preferential growth of Gd2O3 with oriental relationship with substrate GaAs as Gd2O3 {111}<110>\\GaAs{001}<470> with less than 1.5% of lattice mismatching. Capacitance-voltage (C-V) and current density-voltage (J-V) measurements indicated that the interface was seriously degraded when the anneal temperature exceeded 600 degreesC. The feasibility of Gd2O3 film as a buffer layer for ferroelectric-gate/GaAs structure was proved. (C) 2003 Elsevier Science B.V All rights reserved.