The effects of the self-assembled layers formed by adsorption of 4 4'-thio-bis-benzenethiol from ethanol solutions on p-S1(111) and p-GaAs(1 00) electrodes were examined by EIS AFM and XPS investigations All the experimental data led to the conclusion that the thio-bis-benzenethiolate film spontaneously formed on Si and GaAs surfaces brings about chemical passivation both in air and in solution as well as strong adsorbate-substrate interactions which affect the semiconductor surface state population and the field effects operating in the interfacial region Semiempirical PM3 molecular orbital calculations showed that electronic interaction of the thiolate film with the two semiconducting electrodes can be understood in terms of changes in the local density of the electronic states at the surface (C) 2010 Elsevier Ltd All rights reserved