This 48-page handbook uses insight to explain how PN, zener, and Schottky diodes and bipolar-junction transistors (BJTs) block and conduct current. It starts with how solids and semiconductors behave and how adding impurity dopant atoms alters their behavior. With these concepts in hand, the material then details the operating modalities, characteristics, and response of PN and metal-semiconductor junction diodes and BJTs, including electrostatic behavior, band diagrams, current-voltage translations, capacitances, recovery time, breakdown mechanisms, structural variations, and more. Illustrative figures, equations, and examples complement discussions throughout.