Nanometric electrostatic space charges exist at the metal/molecular film interface due to the displacement of excessive electrons from metal to molecular films. As a result, surface potential is built across the films on metal. The distributions of the displaced electrons and the electronic density of states in films can be determined using the surface potential built. The current-voltage characteristic of tunneling device using polyimide Langmuir-Blodgett films is discussed with taking into account the space charge. (C) 2002 Elsevier Science B.V. All rights reserved.