In this study we demonstrated improved electrical characteristics of Gd2 O3 dielectric thin films on n-GaAs substrate by manipulating wet-chemical clean and (N H4)2 S passivation. With X-ray photoelectron spectroscopy analysis, the HCl-cleaned GaAs surface was characterized to possess oxide species mainly in the form of As2 Ox near the outmost surface and Ga2 Ox with elemental arsenic close to the interface. These undesirable components could be suppressed through rinsing in N H4 OH alkaline solution and then performing sulfidization at 80°C, resulting in alleviating the Fermi level pinning effect on Gd2 O3 GaAs capacitor performance. Higher oxide capacitance and alleviated frequency dispersion at the accumulation/depletion regimes were achieved, accompanied by negligible charge trapping (<100 mV). Accordingly, gate leakage Jg was lowered to ca. 10-5 A cm2 at gate voltage Vg = (VFB +1) V, which was comparable to the recently reported performance of Hf O2 GaAs structure with an ultrathin SiGe interfacial layer. We attributed the electrical improvements to the enhanced stabilization of high- k /sulfur-terminated GaAs interface due to abatement of native oxides and excess arsenic segregation.