The scalability of molecular beam epitaxy grown Ga2O3(Gd2O3)/In0.2Ga0.8As/GaAs with in situ Al2O3 capping layers has been studied, in which the InGaAs surface Fermi level has been unpinned. The electrical and structural properties were improved with rapid thermal annealing to high temperatures of 800 degrees C under N-2 flow. As Ga2O3(Gd2O3) is scaled down to 8.5 nm, the dielectric constant maintained at 14-15, similar to those of thicker oxides, resulting in an equivalent oxide thickness of 2.3 nm. A low gate oxide leakage current density of 10(-9) A/cm(2) at parallel to V-G-V-fb parallel to=1, small flatband voltage shift (Delta V-fb), low interfacial density of states (D-it) of (1-3)x10(11) cm(-2) eV(-1) have been achieved. (C) 2008 American Vacuum Society.