Since the arrival of the transistor in 1947, research in hot electrons, like any field in semiconductor research, has grown at a stunning rate. From a physicist's point of view the understanding of hot electrons and their interactions with the lattice has always been a challenging problem of condensed matter physics. Recently, with the advent of novel fabrication techniques such as electron beam or plasma etching and the advanced growth techniques such as the molecular beam epitaxy (MBE) and metallo-organic chemical vapour deposition (MOCVD), it has become possible to fabricate semiconductor devices with sub-micron dimensions where the electrons are confined to two (quantum well), one (quantum wire) or zero (quantum dot) dimensions. In devices of such dimensions a few volts applied to the device result in the setting up of very high electric fields, hence a substantial heating of electrons. Thus electronic transport in the device becomes non- linear and can no longer be described using the simple equations of Ohm's law. The understanding of the operations of such devices, and the realisations of more advanced ones make it necessary to understand the dynamics of hot electrons. There is an obvious lack of good reference books on hot electrons in semiconductors. The few that exist either cover a very narrow field or are becoming quite outdated. This book is therefore written with the aim of filling the vacuum in an area where there is much demand for a comprehensive reference book. The book is intended for both established researchers and graduate students, and gives a complete account of the historical development of the subject, together with current research interests and future trends. The contributions are written by leading scientists in the field. They cover the physics of hot electrons in bulk and low dimensional device technology. The material is organised into subject area that can be classified broadly into five groups: (1)introduction and overview, (2)hot electron phonon interactions and the ultra-fast phenomena in bulk and two dimensional structures, (3)hot electrons in both long and short quantum wires and quantum dots, (4) hot electron tunnelling and hot electron transport in superlattices, and (5) novel devices based on hot electron transport. The chapters are grouped according to subject matter as far as possible. However, although there is much overlap of ideas and concepts, each chapter is essentially independent of the others.