Which of these is a semiconductor amplifying device?

The story behind the answer

Transistors are semiconductor devices with three terminals (e.g., base, collector, emitter in BJTs; gate, source, drain in FETs) that let a small input signal control a much larger output—providing true amplification. They’re built from p-n junctions but, unlike a simple p–n junction diode (two terminals), they can deliver power gain. A diode typically rectifies current and cannot amplify. A “tube” can amplify, but it’s a vacuum tube, not a semiconductor.

Invented in 1947 at Bell Labs, transistors replaced bulky, fragile tubes, enabling modern electronics from radios to smartphones. Memory tip: amplification needs control over a separate path—think “transistor = transfer + resistor,” transferring control from a small signal to a larger one. Also remember: three-terminal semiconductor for amplification = transistor; two-terminal rectifier = diode; tube amplifies, but it’s not semiconductor.