Heterostructures are heterogeneous semiconductor structures built from two or more different semiconductors, in such a way that the transition region or interface between the different materials plays an essential role in any device action. Often, it may be said that the interface is the device.

The unifying concept underlying all heterostructure physics is the idea that energy gap variations act as quasi-electric forces on the electrons and holes in the structure, even in the absence of a true electric field. They give the device designer a new degree of freedom in designing structures exhibiting phenomena fundamentally unobtainable in homostructures.

The possible combinations of two or more semiconductors into a heterostructure are constrained by bonding considerations, both with regard to bond length compatibility (lattice matching) and valence compatibility. In quantized structures, strain may be a deliberate design element.

A useful classification of heterostructures is by lineup type, distinguishing straddling, staggered, and broken-gap lineups. Examples of each type are discussed.

Heterostructure devices are now dominating much of high-speed communication electronics, and they form the very basis of opto-electronics. In communication electronics, the industrial impact of heterostructure devices arises largely from the large economic system leverage they provide through superior performance compared to mainstream silicon devices, more than by manufacturing volumes approaching those of silicon technology. In opto-electronics, light-emitting devices make entirely new applications possible, and are rapidly replacing incandescent lamps; they are likely to reach manufacturing volumes similar to those of silicon integrated circuits.