The transport of mobile sodium ions to the interface in a metaloxide‐semiconductor capacitor causes gross distortions of the capacitance‐voltage characteristics. While these changes might be interpreted as increased surface‐state densities, this paper shows experimentally that the surface‐state densities are unchanged by mobile ion concentrations in the 1012/cm2 range. By comparison of high‐ and low‐frequency capacitance vs. voltage measurements and conductance vs. voltage measurements, it is shown that the distortion of C‐V curves can be explained by fluctuations imposed on the surface potential by a nonuniform pileup of sodium ions at the interface. This argument is further supported by a theoretical reproduction of the experimental C‐V curves obtained by a statistical summation of ideal curves.