The final chapter aims at illustrating to the reader how to build on the concepts introduced in this textbook to understand a wide variety of semiconductor devices, going far beyond the pn-junction devices examined in Chaps. 12 – 14 . To achieve this goal, two types of devices are examined: bipolar junction transistors (BJTs) and field-effect transistors (FETs). The brief discussion focuses on device layouts and band diagrams—both in equilibrium and under applied bias—to illustrate the operation of the two types of transistors. For the bipolar junction transistor, examples of current-voltage characteristics are derived and key properties such as the current amplification factor defined. Among the presented field-effect devices is the junction field-effect transistor (JFET) and the metal-oxide-semiconductor field-effect transistor (or MOSFET)—perhaps the most important semiconductor device for modern information technology. Underlying principles such as the inversion of the channel by the field effect are examined and the main features of the output characteristics described. The chapter concludes with a brief survey of other field-effect devices, including thin-film (or junctionless) field-effect transistors, as well as the complementary metal-oxide-semiconductor (CMOS) process.