The resonant tunneling process of electrons through a single self-assembled InAs quantum dot (QD) has been studied by conductive-tip atomic force microscopy. The unique structure employed here consists of two layers of InAs QDs, which are separated by 5-nm-thick undoped GaAs layer. The conductive tip is placed in contact with the surface InAs QD which functions as a nano-sized electrode to measure the flow of electrons from the n(+)-GaAs substrate via a buried QD. A conductance structure attributed to resonant electron tunneling through the quantized level of QD is observed in the current-voltage characteristics. The resonant voltage is larger than the usual flat band voltage, indicative of a considerable voltage loss caused by the Fermi level pinning around the nano-sized electrode. © 2005 Elsevier B.V. All rights reserved.