The electrical characteristics of titanium dioxide films deposited on p-type gallium arsenide substrate by metallorganic chemical vapor deposition (MOCVD) were studied. For gallium arsenide with ammonium sulfide treatment, the electrical characteristics are improved due to the reduction of interface state density. The electrical characteristics can be further improved by the postmetallization annealing. Hydrogen from the postmetallization annealing process can passivate the defects and the grain boundary of polycrystalline titanium dioxide films. The leakage current densities can reach 2.5 x 10(-7) and 5 x 10(-7) A/cm(2) under positive and negative electric fields at 1.5 MV/cm, respectively. The dielectric constant and effective oxide charges are 66 and 1.86 x 10(12) C/cm(2), respectively. The interface state density is 5.96 x 10(11) cm(-2) eV(-1) at the energy of 0.7 eV from the edge of the valence band. (c) 2006 The Electrochemical Society.