An unpinned interface between an Al2O3 layer deposited by atomic layer deposition (ALD) and a chemically treated n-In0.53Ga0.47As(001) is demonstrated. The starting surface was prepared by wet etching with NH4OH(aq) followed by a thermal desorption of residual As at 380 degrees C immediately before ALD. Analysis of temperature-dependent capacitance-voltage measurements suggests that the Fermi level can sweep through the bandgap of In0.53Ga0.47As, attaining true accumulation and inversion despite the presence of In oxide and In hydroxide at the interface. This is in contrast to the situation for residual As-related interfacial species, which have been reported to pin the Fermi level at oxide/III-V interfaces.