A transistor is a little electronic switch capable of amplifying electric current, invented by John Bardeen, Walter Brattain and William Shockley at Bell Labs in New Jersey on Dec. 16, 1947. They jury-rigged the first transistor using a paper clip, some germanium and gold foil, and found that it boosted electrical current a hundredfold. They kept the discovery to themselves for a bit, and showed their bosses the device just before Christmas. Bardeen, Brattain and Shockley won the Nobel Prize for physics in 1956.
Of course, I've mentioned this earlier in the context of the most under-rated physicist of them all, John Bardeen, who I consider to be http://physicsandphysicists.blogspot.com/2006/09/most-influential-physicist.html.