This book is primarily a manual of circuits based on discrete semiconductor components such as diodes, transistors, FETs, and associated devices, and as such, it presents a total of over 340 carefully selected and useful practical circuits, diagrams, graphs and tables. The manual is divided into four sections, and a total of twelve chapters headings. The first chapter deals with ordinary diode and rectifier circuits, and the second with special diodes such as zeners, varicaps, and photo-sensitive and light-emitting types. The second section comprises five chapters (Chapters 3 to 7) and deals with modern bipolar transistors. The third comprises four chapters (chapters 8 to 11) and deals with major types of field-effect transistor (including the JFET, MOSFET and VMOS). The final chapter deals with the unijunction transistor (UJT) and some of its thyristor counterparts (such as the PUT, SUS and SCS). The book is specifically aimed at the practical design engineer, technician, and experimenter, but will also be of interest to the electronics student and the amateur.