The Atomic Force Microscope used in resonant mode is a powerful tool to measure local surface properties : for example, the quantitative analysis of the electrical forces induced by the application of an electrical tension between a conductive microscope tip and a surface in front allows the determination of the tip/surface capacitance and of the local surface work fonction. However, this analysis needs a well adapted model for each type of surface. In this paper, we calculate, with a simple geometrical model, the tip-surface interaction for a metallic tip and a semiconducting surface and we describe its variation with the applied tension and the tip/surface distance. Our results show different kinds of behaviour that we are able to associate with the different semiconductor regimes (accumulation, depletion, inversion). Therefore, it is not possible to describe this tip-surface system as a passive capacitance