This is a new printing of a popular text, previously published by Prentice Hall in 1994, offering a thorough introduction to the underlying physics of semiconductor devices. It begins with a review of basic solid state physics, then goes on to describe the properties of semiconductors (energy bands, the concept of effective mass, carrier concentration and conduction) in more detail. Chapters 5 & 6 are concerned with the principles of operation of the Gunn Diode and the p-n junction. The remaining chapters focus on specific devices, including the LED, the bipolar transistor, the field-effect transistor and the semiconductor laser. The book concludes with a chapter providing a brief introduction to quantum theory. The book has been specifically written with a view to assisting undergraduates in the first year of their electronic engineering or applied physics degree course. It is not overly mathematical, and places emphasis on only the required physical concepts. Each chapter contains a set of worked problems.