A semiconductor is a material that has the value of the electrical conductivity between that of a conductor and an insulator. Unlike metals, the electrical resistance decreases as the temperature increases in semiconductors. Silicon, germanium and compounds of gallium are commonly used semiconducting materials. The charge carriers in such materials are electrons, ions and electron holes. By controlling the introduction of impurities into their crystal structures, their conducting properties can be altered to suit requirements. This textbook is a compilation of chapters that discuss the most vital concepts in the field of semiconductor physics. It elucidates new techniques and applications of semiconductors in a multidisciplinary manner. It will serve as a valuable source of reference for physicists, engineers and students associated with this important discipline.