The dimensions of modern semiconductor devices are reduced to the point where the classical semiconductor theory, including the concepts of continuous particle concentration and continuous current, becomes questionable. Further questions relate to the two-dimensional transport in the mostimportant field-effect devices and the one-dimensional transport in nanowires and carbon nanotubes.Designed for upper-level undergraduate and graduate courses, Principles of Semiconductor Devices, Second Edition, presents the semiconductor-physics and device principles in a way that upgrades the classical semiconductor theory and enables proper interpretations of numerous quantum effects inmodern devices. The semiconductor theory is directly linked to practical applications, including the links to SPICE models and parameters that are commonly used during circuit design. The text is divided into three parts: Part I explains semiconductor physics; Part II presents the principles of operation and modeling of the fundamental junctions and transistors; and Part III provides supplementary topics, including a dedicated chapter on the physics of nanoscale devices,description of SPICE models and equivalent circuits that are needed for circuit design, introductions to most important specific devices (photonic devices, JFETs and MESFETs, negative-resistance diodes, and power devices), and an overview of integrated-circuit technologies. The chapters and thesections in each chapter are organized so to enable instructors to select more rigorous and design-related topics as they see fit.