Polar interfaces between semiconductors are shown to have a tendency to form reconstructed compensated interfaces with no free carriers. The conditions for stability of such interfaces are given in terms similar to that for self-compensation in bulk cases, and it is shown that all GaAs–Ge interfaces are expected to obey the conditions. Electronic calculations are given for reconstructed (100) interfaces. The reconstructions can be described by atomic substitutions in the interface layers, which are shown to be examples of general models for order–disorder in two dimensions. The nature of the order is discussed for (100) and (111) interfaces, and it is predicted that there will be ordered charges but disordered dipoles in the interface layers.