Jun-ichi Nishizawa (西澤 潤一, Nishizawa Jun'ichi; September 12, 1926 – October 21, 2018) was a Japanese engineer and inventor. He is known for his electronic inventions since the 1950s, including the PIN diode, static induction transistor, static induction thyristor, SIT/SITh. His inventions contributed to the development of internet technology and the Information Age. He was a professor at Sophia University.

Nishizawa was born in Sendai, Japan, on September 12, 1926. He earned a B.S. in 1948, and a Doctor of Engineering degree in 1960, from Tohoku University.

In 1953, he joined the Research Institute of Electrical Communication at Tohoku University. He became a professor there and was appointed director to two research institutes. From 1990 to 1996, Nishizawa served as the President of Tohoku University.

He became the president of Iwate Prefectural University in 1998.

In 1950, the static induction transistor was invented by Jun-ichi Nishizawa and Y. Watanabe. The PIN photodiode was also invented by Nishizawa and his colleagues in 1950.

In 1952, he invented the avalanche photodiode. He then invented a solid-state maser in 1955. This was followed by his proposal for a semiconductor optical maser in 1957, a year before Schawlow and Townes's first paper on optical masers.

While working at Tohoku University, he proposed fiber-optic communication, the use of optical fibers for optical communication, in 1963. Nishizawa invented other technologies in the 1960s that contributed to the development of optical fiber communications, such as the graded-index optical fiber as a channel for transmitting light from semiconductor lasers. He patented the graded-index optical fiber in 1964.

In 1971, he invented the static induction thyristor.