What is a bias resistor built-in transistor?

A bias resistor built-in transistor (BRT) is a bipolar transistor with a bias network consisting of a series base resistor and a base-emitter resistor. With bias resistors built into the transistor, BRTs help reduce the number of external components required, simplifying a discrete circuit configuration. BRTs are commonly used for switching applications.

Recently, there is a tendency to use MOSFETs instead of transistors with built-in resistors owing to their high-speed switching, low current consumption, on-voltage, low drive voltage, etc.