In this paper, an electrochemical impedance study of the Ge/electrolyte interface has been carried out. At n-type Ge (100) and Ge (111) electrodes with different donor densities, linear Mott-Schottky plots were observed over a wide potential region, showing that the depletion region is conserved up to a band bending exceeding the bandgap of Ge. In most cases, the Mott-Schottky plots show some frequency dependence. A more elaborate investigation of the total interfacial impedance using electrochemical impedance spectroscopy shows that this frequency dependence may be caused by an additional impedance in parallel with the depletion layer capacity in the equivalent circuit describing the Ge/electrolyte interface. Under very weak depletion conditions, i.e., close to the flatband potential, an additional impedance is also observed, which may be related to electron-hole recombination at the semiconductor surface. For p-type Ge electrodes, linear Mott-Schottky plots are much more difficult to obtain, probably because electrochemical reactions and/or surface recombination strongly complicate the total impedance of the Ge/electrolyte interface. (C) 2008 The Electrochemical Society.