"You probably should talk to my lawyer," Xi, a naturalized U.S. citizen born in China, said to a reporter after Thursday's arraignment.
Xi has hired Peter R. Zeidenberg, a Washington lawyer who successfully had all charges against an Ohio woman accused of spying for China dropped in March. Xi faces up to 80 years in prison and a $1 million fine if convicted.
"Professor Xi is innocent of these charges and expects that he will ultimately be fully exonerated," Zeidenberg, a partner at Arent Fox L.L.P., said in an e-mail.
Xi, dressed in a dark pinstripe suit, stood Thursday to enter his plea. He was accompanied by his wife to the federal courthouse. The couple live in Penn Valley with their two children.
As part of his release, Xi's travel was restricted to nine counties in Southeastern Pennsylvania. He had to surrender any passports.
Prosecutors said Xi, in 2002, worked at a U.S. company that invented a device that revolutionized his field. A year later, he purchased the device for one year to continue his testing. But, prosecutors allege, he violated the agreement not to reproduce, sell, transfer, or attempt to reverse-engineer it.
They cited several e-mails Xi sent in 2010 to Chinese contacts. Xi, authorities said, offered to build a world-class thin-film laboratory in China.
The FBI's investigation is ongoing, a U.S. Attorney's Office spokeswoman said Thursday.
Following the charges, Temple demoted Xi from his chairman position. University officials have said Xi will remain on the faculty, but no decision has been made as to whether Xi would be allowed to continue teaching in the fall.
Before coming to Temple in 2009, Xi gained prominence with research on superconductive magnesium diboride thin films while on the faculty at Pennsylvania State University.
Such research allows engineers to eliminate resistance in the conduction of electricity. It has applications ranging from building smaller circuits for smartphones to improving speed in computers. The research also has military applications.