Xiaoxing Xi (Chinese: 郗小星; pinyin: Xī Xiǎoxīng; born 1957) is a Chinese-born American materials physicist specializing in the electromagnetic properties of thin films. He is the Laura H. Carnell Professor and former chair at the Physics Department of Temple University in Philadelphia. In May 2015, the United States Department of Justice arrested him on charges of having sent restricted American technology to China. All charges against him were dropped in September 2015.

Xi was born in China and grew up during the Cultural Revolution. He matriculated to the physics department at Peking University in 1978 as part of the first class following the Cultural Revolution. He graduated with a BSc in physics in 1982. He studied under Weiyan Guan, and received his PhD in 1987 for work in superconductivity.

Following graduate studies, Xi was a researcher at the Karlsruhe Nuclear Research Center in Germany, where he worked on epitaxial yttrium barium copper oxide thin films. Thirumalai Venkatesan visited Karlsruhe and made offers to both Xi and his wife, who is also a physicist, to come work with him at Bell Communication Research at Rutgers University. Xi and his wife accepted Venkatesan's offer and moved to the United States in 1989. When Venkatesan moved to the University of Maryland five years later, Xi and his wife moved as well. While at Maryland Xi researched high-temperature superconductor field-effect transistors.

In 1995 Xi's wife received an offer from Pennsylvania State University and Xi received an offer as the spousal hire. There Xi shifted his research to ultrathin ferromagnetic films. Xi's wife is still a physics professor at Pennsylvania State University. While at Pennsylvania State University, Xi was nominated as a fellow of the American Physical Society by the Division of Materials Physics "for his extensive and seminal contributions to the science and applications of thin film materials including high temperature superconductors, ferroelectrics, and magnesium diboride."

In 2009 Xi became a professor at Temple University. Xi was named chairman of Temple University's physics department in 2014.

Xi has naturalized as a US citizen. He and his wife have two daughters and live in suburban Philadelphia.

In 2015, police raided Xi's home and arrested him at gunpoint in front of his wife and two daughters. The US Justice Department (DOJ) had accused the scientist of illegally sending trade secrets to China: specifically, the design of a pocket heater used in superconductor research. Xi was indicted on four counts of wire fraud, putting him under threat of 80 years in prison and $1 million in fines. Xi's daughter Joyce Xi said, "newscasters surrounded our home and tried to film through windows. The FBI rummaged through all our belongings and carried off electronics and documents containing many private details of our lives. For months, we lived in fear of FBI intimidation and surveillance. We worried about our safety in public, given that my dad's face was plastered all over the news. My dad was unable to work, and his reputation was shattered."

Temple University forced Xi to take administrative leave and suspended him as chair of the Physics Department. He was also banned from accessing his lab or communicating with his students directly. It was later learned that FBI agents had been listening to his phone calls and reading his emails for months — possibly years.