Transistors: Bipolar Junction Transistors (BJT) General configuration and definitions The transistor is the main building block “element” of electronics.It is a semiconductor device and it comes in two general types: the Bipolar Junction Transistor (BJT) and the Field Effect Transistor (FET).Here we will describe the system characteristics of the BJT configuration and explore its use in fundamental signal shaping and amplifier circuits.The BJT is a three terminal device and it comes in two different types. The npn BJT and the pnp BJT.The BJT symbols and their corresponding block diagrams are shown on Figure 1. The BJT is fabricated with three separately doped regions.ransistors: Bipolar Junction Transistors (BJT) General configuration and definitions The transistor is the main building block “element” of electronics.