Measurement of the interfacial capacity of germanium electrodes in aqueous solutions of pH 4.5–11.5 permits the determination of the potential difference (p.d.) across the semiconductor space charge region . Hence, under changing conditions, changes in the p.d. across the Helmholtz region may be deduced since where is the electrode potential on an arbitrary scale. The steady‐state value of depends on anodic current density. The values of corresponding to a fixed current density vary by about 59 mv per decade of hydrogen ion concentration. This supports a recent view that a “dissociation double layer” is formed by the pH dependent ionization of surface hydroxyl groups. For solutions more acid than pH 4.5 and more alkaline than pH 11.5 the data indicate that considerable densities of fast surface states occur.