We investigate the wet chemical cleaning process of GaAs substrate for ready-to-use. To prepare epi-ready GaAs wafer, we used NH4OH mixture to remove particles and metals as a first step of wet-chemical cleaning and acidic peroxide mixture to remove residual metallic contaminants and control the components of oxide layer as a second step of wet-chemical cleaning. The particle-free, metal-free, and thin As-oxide rich surface is achieved by the proposed ratio of NH4OH mixture followed by HCl mixture among the second step of wet-chemical cleaning solution used in this experiment. Metal-contamination was analyzed by total reflection X-ray fluorescence spectroscopy. Characterization of the oxide composition was carried out by X-ray photoelectron spectroscopy. Surface morphology and thickness of oxide layer were observed by atomic force microscopy and ellipsometer, which show very flat surface roughness of 0.95 nm, and uniform oxide thickness of about 2 nm, respectively. (C) 2004 Elsevier B.V. All rights reserved.