Mechanical polishing and etching in acids or molten of electrodes frequently lead to nonlinear Mott‐Schottky plots. These surface treatments are discussed in relation to surface roughness effects and the occurrence of nonuniform donor distributions. Modified Mott‐Schottky equations are presented and discussed. They account quantitatively for surface roughness and nonuniform donor distributions, which can be induced not only by etching, but also by anodical aging, surface doping, reoxidation effects, and cathodical loading with hydrogen.