Electron tunneling is investigated for the alkanethiol self-assembled monolayers (SAMs) formed using three different device structures spanning from the nanometer to the micrometer scale. The measured current-voltage characteristics for the alkanethiol SAMs can be explained by the classical metal-insulator metal tunneling model and the tunneling current exhibits overall exponential trend on the molecular length. Although different structures give consistent results (such as decay coefficient), unambiguous determination of the tunneling requires characterization of length and temperature dependencies. (C) 2004 Elsevier B.V. All rights reserved.