A type of breakdown that occurs in a semiconductor. It is caused by the cumulative multiplication of free charge carriers under the action of an applied electric field. Some of the carriers gain enough energy to liberate new electron-hole pairs by impact ionization, which in turn can generate further pairs, i.e. an avalanche takes place.

The avalanche process occurs when a critical field is reached across the semiconductor. The critical field is the voltage gradient that just causes avalanche in a given specimen of semiconductor and is typical for the material used. For a given semiconductor the value of the applied voltage required to produce the critical field – the breakdown voltage – is a function of the doping concentration and the thickness of the specimen.

Avalanche breakdown is the breakdown that occurs in a reverse-biased p-n junction. For a given junction the breakdown voltage is a function of the doping concentrations on each side of the junction and on the width of the depletion layers associated with the junction. A more highly doped junction has a lower value of breakdown voltage than a junction with lighter doping. The avalanche process is initiated by carriers contributing to the small reverse saturation current.