What did Walter Brattain invent?

John Bardeen, Walter Brattain and William Shockley worked together at Bell Labs in the 1940s for a relatively brief period of time. But their collaboration resulted in one of the most important inventions of the century: the transistor. This device would transform the electronics world and make a major impact on the architecture of computers, helping to put them into the mainstream just a few years later. Taken from Inventor of the Week