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Measurements have been made of the electrode potential of p‐ and n‐type germanium in contact with aqueous solutions of KOH, KCl and HCl as a function of anodic and cathodic current and of incident light intensity. For anodic currents, the measured electrode potential can be separated into three parts: the reversible electrode potential corresponding to the anodic reaction, depending only on the solution; an overvoltage of the usual form; and a term (kT/e) In (p1/p), where p is the equilibrium hole concentration and p1 is the concentration just inside the space‐charge region of the germanium. The anodic current is determined by flow of holes to the surface, so that the current saturates for n‐type germanium but not for p‐type. The saturation current is determined by body and surface generation of holes and by creation of excess holes by light. There is a current gain of 1.4 to 1.8. In addition, there is a small “leakage” current not dependent on hole supply. Similar statements may be made for cathodic current, except that the electrode potential and current arc determined respectively by the concentration and supply of electrons instead of holes, the current gain is of the order of unity, and the leakage current is larger. Complicating time changes were observed for cathodic but not for anodic currents. The measurements may be understood in terms of simple thermodynamic considerations, based on the idea that the anodic reaction is with holes, the cathodic reaction with electrons, in the semiconductor; the behavior for very small currents depends on a competition between the anodic and cathodic reactions, which may be treated by simple rate process considerations. A comparison is made with experiments on the germanium‐gas interface by Brattain and Bardeen, to which similar considerations may apply.

The properties associated with the space-charge region and with surface states at a semiconductor surface are discussed. A theory of the space-charge region that takes into account charge-densities arising from immobile impurities and from both signs of mobile carrier is presented. The properties of the space-charge are discussed in terms of the surface potential and of the electrochemical potentials of holes and electrons, and related to the transport of added carriers in a homogeneous semiconductor. The change in surface conductivity arising from nonvanishing surface excesses of holes and electrons is treated. The space-charge systems at a free surface and at a p-n junction are compared, and the range of validity of the Mott-Schottky space-charge theory evaluated. The arrangement of surface states is discussed with reference to the Brattain-Bardeen model. Theories for the surface photoeRect and field-effect experiments are given, with and without surface states: it is concluded that the existence of surface states is without gross effect on the former, while relevant quantitative evidence from the latter is not yet available. The question of the relation between surface potential and contact potential is discussed. The properties of "channels" are discussed in terms of the theory. The paper concludes with a short section on long-time effects.