Almost every undergraduate engineering discipline starting from electronics, electrical, computer science, instrumentation engineering, information technology, mechanical engineering, biotechnology etc. requires a solid foundation in basic electronics which comprises a study of fundamental devices like diodes, transistors and their applications in designing amplifiers, switching/logic circuits etc. While for some disciplines, a basic understanding might be sufficient, for other disciplines like electronics, electrical etc., this course acts as an important building block in the curriculum. Moreover, for various advanced courses like analog electronics, digital circuits and VLSI, in-depth understanding of basic electronics is a prerequisite. This book is written keeping both these aspects in mind and as a result it will serve undergraduate students of various engineering disciplines. In addition, it can also cater to the needs of college and university students belonging to disciplines like physics, electronics, and also in electronics courses in polytechnics. A competent electronics engineer, even in the modern era of integrated-circuit based design, needs a thorough and solid understanding of the basic concepts of semiconductors and a firm grasp of fundamental devices like diodes and various kind of transistors. This book attempts a perfect balance between housing all the basic concepts in accordance with the syllabi of leading institutes and universities and a thorough understanding required for future courses. In solid state electronics and analog electronics, which normally appears at a later stage of the undergraduate electronics curriculum, the approach is significantly different: while solid state electronics provides more emphasis on device physics and detailed understanding, analog electronics concentrates more on the applications, where the device is generally treated as a black box. Even though these two advanced courses are mutually dependent on each other, there exists a significant gap between the two approaches and undergraduate students face real difficulties in making a correlation and correspondence between them. This book attempts to minimize this gap between the different approaches to solid state devices and analog circuits. Special care has been taken to explain all the semiconductor devices in this book from both, physical and circuit approaches. To facilitate this, extra stress is given in chapters 2 and 3 while discussing crystal structures and the p-n junctions. As all modern semiconductor devices are based on clusters of p-n junctions, a detailed explanation about the various aspects of p-n junctions will provide readers a strong foundation for future courses.