The surface of silicondioxide/silicon structures is charged with the tip of a cantilever in contact mode by application of a voltage. Then, the surface potential is measured contactless using the Kelvin option of an atomic force microscope. On the position of the charged domain a potential difference in relation to the uncharged region is found. It turns out that the height and the width of this potential difference depend on the charging time, on the height of the charging voltage, on the sample thickness, and on the doping of the siliconsubstrate. Furthermore, a time dependent spread and a decay of the surface potential are observed. For dry samples the decay is slower than for wetted samples. Due to this long-term stability at dry samples and the possibility to reverse the sign of the deposited charge by recharging in opposite direction it is thinkable to use the system as a surface charge memory device.