This book presents the fundamental quantum processes involved in the physics and technology of semiconductors. Its relatively informal style makes it an ideal introduction for graduate courses as well as a reliable reference for researchers in the field. This edition has been expanded to include new chapters on quantum transport, semi-classical transport and space-charge waves, extending the discussion to statistical, many-particle behavior in transport phenomena. The author has also taken the opportunity to update other sections. As with previous editions the text restricts its attention to bulk semiconductors. It traces the path from quantum processes describable by density matrices, through the semi-classical Boltzmann equation and its solutions, to the drift-diffusion description of space-charge waves, the latter appearing in the contexts of negative differential resistance, acoustoelectric and recombination instabilities.