This paper investigates the behavior of the space charge region of a silicon solar cell and its associated capacitance under the effect of an external electric field. In steady state and under dark conditions, the space charge region width is mainly given by the doping concentration of both p and n regions of the cell. The purpose of this work is to show that under illumination the solar cell’s space charge region width varies with both operating point and the external induced electric field and also how the solar cell capacitance varies with the space charge region width.