Designed as a text for undergraduate students of engineering in Electrical, Electronics, and Computer Science and IT disciplines as well as undergraduate students (B.Sc.) of physics and electronics as also for postgraduate students of physics and electronics, this compact and accessible text endeavours to simplify the theory of solid state devices so that even an average student will be able to understand the concepts with ease. The authors, Prof. Somanathan Nair and Prof. S.R. Deepa, with their rich and long experience in teaching the subject, provide a detailed discussion of such topics as crystal structures of semiconductor materials, Miller indices, energy band theory of solids, energy level diagrams and mass action law. Besides, they give a masterly analysis of topics such as direct and indirect gap materials, Fermi–Dirac statistics, electrons in semiconductors, Hall effect, PN junction diodes, Zener and avalanche breakdowns, Schottky barrier diodes, bipolar junction transistors, MOS field-effect transistors, Early effect, Shockley diodes, SCRs, TRIAC, and IGBTs