At Bell Labs in 1947, what type of transistor was demonstrated by John Bardeen and Walter Brattain?

John Bardeen and Walter Brattain demonstrated the point-contact transistor at Bell Labs in 1947.

Their device used two closely spaced metal contacts pressed against a small piece of germanium. A signal applied at one contact could control a larger current between the contacts, allowing amplification and switching without the fragile heated cathode used in vacuum tubes.

Bardeen and Brattain demonstrated the transistor effect on 16 December 1947, and a public demonstration followed in 1948. William Shockley, also at Bell Labs, later developed the more practical bipolar junction transistor, which became easier to manufacture and widely used.

The point-contact transistor is therefore historically important even though it was not the dominant long-term design. The invention began the solid-state electronics revolution, leading to smaller radios, computers, integrated circuits, and modern digital devices.