A transistor is a semiconductor device with at least three terminals for connection to an electric circuit. In the common case, the third terminal controls the flow of current between the other two terminals. This can be used for amplification, as in the case of a radio receiver, or for rapid switching, as in the case of digital circuits. The transistor replaced the vacuum-tube triode, also called a (thermionic) valve, which was much larger in size and used significantly more power to operate.The first transistor was successfully demonstrated on December 23, 1947, at Bell Laboratories in Murray Hill, New Jersey. Bell Labs was the research arm of American Telephone and Telegraph (AT&T). The three individuals credited with the invention of the transistor were William Shockley, John Bardeen and Walter Brattain. The introduction of the transistor is often considered one of the most important inventions in history. Transistors are broadly classified into two categories: bipolar junction transistor (BJT) and field-effect transistor (FET). The principle of a field-effect transistor was proposed by Julius Edgar Lilienfeld in 1925. John Bardeen, Walter Brattain and William Shockley invented the first working transistors at Bell Labs, the point-contact transistor in 1947. Shockley introduced the improved bipolar junction transistor in 1948, which entered production in the early 1950s and led to the first widespread use of transistors. The MOSFET (metal–oxide–semiconductor field-effect transistor), also known as the MOS transistor, was invented by Mohamed Atalla and Dawon Kahng at Bell Labs in 1959. MOSFETs use even less power, which led to the mass-production of MOS transistors for a wide range of uses. The MOSFET has since become the most widely manufactured device in history. Origins of transistor concept The first patent for the field-effect transistor principle was filed in Canada by Austrian-Hungarian physicist Julius Edgar Lilienfeld on October 22, 1925, but Lilienfeld published no research articles about his devices, and his work was ignored by industry. In 1934 German physicist Dr. Oskar Heil patented another field-effect transistor. There is no direct evidence that these devices were built, but later work in the 1990s show that one of Lilienfeld's designs worked as described and gave substantial gain. Legal papers from the Bell Labs patent show that William Shockley and a co-worker at Bell Labs, Gerald Pearson, had built operational versions from Lilienfeld's patents, yet they never referenced this work in any of their later research papers or historical articles. The