The atomic layer deposition (ALD) of Al2O3 using trimethylaluminum (TMA) as a metal precursor on an InSb substrate with or without surface pretreatments was investigated. It was found that both in situ TMA/Ar purging (half-ALD cycle) and ex situ CP4A (HNO3:HF:CH3COOH:H2O=2:1:1:10) chemical etching can remove the native oxides on InSb before ALD of Al2O3, and lead to a native-oxides-free Al2O3/InSb structure. Characteristics of current density-voltage and capacitance-voltage were also investigated to evaluate the insulative and interface quality in a Pt/Al2O3/InSb metal-oxide-semiconductor structure. (C) 2008 The Electrochemical Society.