The chemical and morphological properties of thin aluminum oxide film surfaces (Al2O3 having 10 nm in thickness) in the as-deposited (dry) and after immersion (in pH buffer solutions) conditions were studied. Careful measurement conditions have been followed in order to determine any possible physical and/or chemical change on the surface of these films (after immersion in pH), so that proper correlation to their high and stable sensitivity to pH is possible. After deposition of thin Al2O3 films (by Atomic Layer Deposition, ALD) on chemically oxidized p-type silicon wafers, the resulting Al2O3/SiOX/Si stacked structures were characterized by Fourier-Transform Infrared Spectroscopy (FTIR) and Atomic Force Microscopy (AFM) before and after immersion in pH buffer solutions. Also, the Capacitance-Voltage (C-V) and Current-Voltage (I-V) characteristics were obtained after fabrication of Metal-Insulator-Semiconductor (MIS) devices in order to correlate the good chemical and morphological characteristics of thin Al2O3 to its electrical properties. Based on the characterization results, low surface oxidation/dissolution mechanisms are found in ALD aluminum oxide films when immersed in pH buffer solutions during short immersion times (immersion time <= 10 minutes); therefore, leading to the characteristic slow degradation of the sensitivity to pH for this dielectric material. (C) 2013 The Electrochemical Society. All rights reserved.