The U.S. patent number for the first transistor invented in 1947 was 2,524,035.
John Bardeen and Walter Brattain built the first working point-contact transistor at Bell Labs in December 1947, using two gold contacts pressed against a germanium crystal. William Shockley, their group leader, helped develop the theory and later created the junction transistor.
Patent 2,524,035 was titled “Three-electrode circuit element utilizing semiconductive materials.” Although the device was demonstrated in 1947, the patent was not granted until October 3, 1950, after its 1948 filing. That delay is a common source of confusion in trivia questions about the transistor.
The first transistor was not the silicon component familiar in modern computers. It used germanium and was relatively delicate. Silicon transistors became practical later, including the first working silicon transistor demonstrated at Bell Labs in 1954. Bardeen, Brattain, and Shockley shared the 1956 Nobel Prize in Physics for their work on semiconductors and the transistor effect.