Self-aligned inversion-channel In0.53Ga0.47As n-MOSFETs with ex-situ atomic-layer-deposited Al2O3 and in-situ ultra-high-vacuum deposited Al2O3/Ga2O3(Gd2O3) as gate dielectrics have been demonstrated. Both devices exhibit excellent DC characteristics, including high drain currents and transconductances. In addition, RF characteristics of both devices were analyzed; without using any isolation, non dc-embedded current gain cutoff frequency (fT) and maximum oscillation frequency (fmax) of ~ 3.1 and 1.1 GHz (ALD-Al2O3) and of ~ 17.9 and 11.2 GHz (MBE-Al2O3/Ga2O3(Gd2O3)), respectively, have been obtained.