A transistor radio is a small portable radio receiver that uses transistor-based circuitry. Previous portable radios used vacuum tubes, which were bulky, fragile, had a limited lifetime, consumed excessive power and required large, heavy batteries. Following the invention of the transistor in 1947—a semiconductor device that amplifies and acts as an electronic switch, which revolutionized the field of consumer electronics by introducing small but powerful, convenient hand-held devices—the Regency TR-1 was released in 1954 becoming the first commercial transistor radio. The mass-market success of the smaller and cheaper Sony TR-63, released in 1957, led to the transistor radio becoming the most popular electronic communication device of the 1960s and 1970s. Billions had been manufactured by about 2012.

The pocket size of transistor radios sparked a change in popular music listening habits, allowing people to listen to music and other broadcasts on the radio anywhere they went. Beginning around 1980, however, cheap AM transistor radios were superseded initially by the boombox and the Sony Walkman, and later on by digitally based devices with higher audio quality such as portable CD players, personal audio players, MP3 players and smartphones, many of which contain FM radios. Transistor radios continue to be built and sold for portable and in-car use but the term "transistor" is no longer used in marketing as virtually all modern technology makes use of transistors.

Before the transistor was invented, radios used vacuum tubes. Although portable vacuum tube radios were produced, they were typically bulky and heavy. The need for a low-voltage, high-current source to power the filaments of the tubes and high voltage for the anode potential typically required two batteries. Vacuum tubes were also inefficient and fragile compared to transistors and had a limited lifetime.

Bell Laboratories demonstrated the first transistor on 23 December 1947. The scientific team at Bell Laboratories responsible for the solid-state amplifier included William Shockley, Walter Houser Brattain, and John Bardeen After obtaining patent protection, the company held a news conference on 30 June 1948, at which a prototype transistor radio was demonstrated.

There are many claimants to the title of the first company to produce practical transistor radios, often incorrectly attributed to Sony (originally Tokyo Telecommunications Engineering Corporation). Texas Instruments had demonstrated all-transistor AM (amplitude modulation) radios as early as 25 May 1954, but their performance was well below that of equivalent vacuum tube models. A workable all-transistor radio was demonstrated in August 1953 at the Düsseldorf Radio Fair by the German firm Intermetall. It was built with four of Intermetall's hand-made transistors, based upon the 1948 invention of the "Transistor"-germanium point-contact transistor by Herbert Mataré and Heinrich Welker. However, as with the early Texas Instruments units (and others) only prototypes were ever built; it was never put into commercial production. RCA had demonstrated a prototype transistor radio as early as 1952, and it is likely that they and the other radio makers were planning transistor radios of their own, but Texas Instruments and Regency Division of I.D.E.A., were the first to offer a production model starting in October 1954.

The use of transistors instead of vacuum tubes as the amplifier elements meant that the device was much smaller, required far less power to operate than a tube radio, and was more resistant to physical shock. Since the transistor's base element draws current, its input impedance is low in contrast to the high input impedance of the vacuum tubes. It also allowed "instant-on" operation, since there were no filaments to heat up. The typical portable tube radio of the 1950s was about the size and weight of a lunchbox and contained several heavy, non-rechargeable batteries—one or more so-called "A" batteries to heat the tube filaments and a large 45- to 90-volt "B" battery to power the signal circuits.

By comparison, transistor radios were smaller and shrank until they could fit in a pocket and weighed half a pound or less. The 1954 radios needed 22½V brick-like prismatic batteries and 1956 radios were the first to run on 9 V, both of whose batteries came in different sizes for capacity and the latter also usually used flat heavy batteries but sometimes can or cylindrical batteries. The common small flat 9-volt battery that went on to dominate the market was popularized by the Sony TR-63 made in 1957 by Tokyo Tsushin Kogyo. The instructions sticker inside specified the battery models that took, those of the small size that had been produced the year earlier:

Two companies working together, Texas Instruments of Dallas, and Industrial Development Engineering Associates (I.D.E.A.) of Indianapolis, Indiana, were behind the unveiling of the Regency TR-1, the world's first commercially produced transistor radio. Previously, Texas Instruments was producing instrumentation for the oil industry and locating devices for the U.S. Navy and I.D.E.A. built home television antenna boosters. The two companies worked together on the TR-1, looking to grow revenues for their respective companies by breaking into this new product area. In May 1954, Texas Instruments had designed and built a prototype and was looking for an established radio manufacturer to develop and market a radio using their transistors. The chief project engineer for the radio design at Texas Instruments' headquarters in Dallas, Texas, was Paul D. Davis Jr., who had a degree in electrical engineering from Southern Methodist University. He was assigned the project due to his experience with radio engineering in World War II. None of the major radio makers including RCA, GE, Philco, and Emerson were interested. The President of I.D.E.A. at the time, Ed Tudor, jumped at the opportunity to manufacture the TR-1, predicting sales of the transistor radios at "20 million radios in three years". The Regency TR-1 was announced on 18 October 1954, by the Regency Division of I.D.E.A., was put on sale in November 1954 and was the first practical transistor radio made in any significant numbers. Billboard reported in 1954 that "the radio has only four transistors. One acts as a combination mixer-oscillator, one as an audio amplifier, and two as intermediate-frequency amplifiers." One year after the release of the TR-1 sales approached the 100,000 mark. The look and size of the TR-1 were well received, but with only four transistors the sound quality was poor, and the reviews of the TR-1's performance were typically adverse. The Regency TR-1 was patented by Richard C. Koch, former Project Engineer of I.D.E.A.