The high Dit is the major problem of III-V compound semiconductor MOSFET, which causes the pinning of the surface Fermi level near the middle of the energy gap. The GaAs with (NH4)2Sx treatment (S-GaAs) can remove the native oxides on GaAs and prevent it from oxidizing. The electrical characteristics of fluorinated polycrystalline TiO2 films deposited on p-type(100) S-GaAs were investigated. The fluorine from liquid phase deposition solution can passivate the grain boundary of polycrystalline TiO2 prepared by MOCVD. The leakage current through the grain boundaries was suppressed. The leakage current of MOCVD-TiO2/S-GaAs can be improved from 6.8 x 10-6 and 0.2 A/cm2 to 3.41 x 10-7 and 1.13 x 10-6A/cm2 under positive and negative electric fields at 1.5 MV/cm, respectively. Dit and k can be improved from 1.44 x 1012 cm-2eV-1 to 4.6 x 1011 cm-2eV-1 and 52 to 65, respectively. The effective oxide charges can be improved from 2.5 x 1012 C/cm-2 to 9.3 x 1011 C/cm-2.