Effects of the self-assembled layers of biphenyl 4,4'-dithiol (BPDT) and 1,8-octanedithiol (ODT) on the chemical and electronic properties of p-doped GaAs (111)-As terminated substrate, (p-GaAs(111)B), were investigated in order to evidence whether the hydrocarbon moiety plays a role in tailoring the semiconductor surface properties. The electrochemical properties of the BPDT and ODT coated p-GaAs(111)B substrates were studied by Electrochemical Impedance Spectroscopy (EIS). The structural and chemical changes caused by the dithiolate layers formed on p-GaAs(111)B substrates were monitored by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) investigations, respectively. The XPS data showed that BPDT and ODT bind to pGaAs(111)B via the thiol group. The ODT layer provides better protection against the further oxidation in air of p-GaAs(111)B substrate compared to the BPDT layer. The EIS investigations are in good agreement with XPS results, pointing to better insulating properties of the ODT layer compared to the BPDT layer in the electron transfer at the electrode/solution interface. The results evidenced that backbone plays an important role in tailoring the properties of p-GaAs(111)B substrate. (C) 2016 Elsevier B.V. All rights reserved.