Recently, we reported the observation of step structure, similar to Coulomb staircase, in the current-voltage characteristic of metal /polyimide(PI) /rhodamine-dendrimer (Rh-G2) PI/ metal junctions prepared by the Langmuir-Blodgett(LB) technique [J. Appl. Phys. 90, 1368 (2001)]. Calculating the additional apparent capacitance formed by electrostatic charge at the interface, the equation of threshold voltage of the step structure was derived and the interfacial space charge effect was pointed out. However, this analysis is not suffcient. In this Addendum, the equation of step voltage is derived taking into account both electrostatic charges and residual charges by electron tunneling. It was found that the derived equation is more satisfactory to explain our previous experimental result.