The electrical characteristics of atomic layer deposited (ALD) Al2O3/TiO2/Al2O3 on (NH4)(2)S treated GaAs MOS capacitor were studied. The electrical characteristics were improved from the reduction of native oxides and sulfur passivation on GaAs by (NH4)(2)S treatment. The top high bandgap ALD-Al2O3 can further reduce the thermionic emission, and the bottom ALD-Al2O3 improves the interface state density by the self-cleaning. The high dielectric constant TiO2 is used to lower the equivalent oxide thickness. The leakage currents can reach 8.3 x 10(-9) and 2.2 x 10(-7) A/cm(2) at +/- 2 MV/cm, respectively. The interface state density is 3.11 x 10(11) cm(-2)ev(-1) at the energy of about 0.57 eV from the edge of the valence band. (C) 2013 Elsevier Ltd. All rights reserved.