The transistor was invented at Bell Laboratories in December 1947 by John Bardeen and Walter Brattain. 'Discovered' would be a better word, for although they were seeking a solid-state equivalent to the vacuum tube, it was found accidentally during the investigation of the surface states around a diode point-contact. The first transistors were therefore of the point-contact type. William Shockley, the theorist who was leading the research, knew at once that this was not what he was seeking: at the time he was trying to create a solid-state device similar to what we now call a junction field-effect transistor (JFET).
Bell Labs kept their discovery quiet until June 1948. They then announced it in a fanfare of publicity, but few people realised its significance, and it did not even make the front page of the newspapers. Shockley basically ignored the point-contact transistor, and continued his research in other directions. He modified his original ideas and developed the theory of the bipolar junction transistor (BJT). In July 1951, Bell announced the creation of such a device. In September 1951 Bell held a transistor symposium, and licensed their technology for both types of transistor to anyone who paid the required fee of 25 thousand dollars. This was the start of the transistor industry that has changed the way that we live, in the Western world at least.
The above is a very brief summary of the discovery of the transistor. Much has been written on the subject, in books and on the Web. See my links page for resources which describe the discovery of the transistor in much more detail. A number of contemporary books describe the subsequent development of the transistor, and later ones document the history of that period, especially the work of Shockley, Bardeen and Brattain at Bell Labs. I have assembled a bibliography of the most interesting of these texts. Follow the links on the left to read my own research in this area, which concentrates on non-US companies, a comparatively neglected area.
Of course I have come across early devices that I cannot find information about. I'd like your help in identifying them. Click on my 'mystery devices' link to see them.