The deal would have meant Dharun Ravi would have served no more than five years in prison.
His lawyers put the offer on the record Thursday before a judge set a Feb. 21 trial date.
The 19-year-old faces 15 charges, including bias intimidation and invasion of privacy.
Ravi could face 10 years in prison if a jury convicts him of bias intimidation, which is a hate crime.
Prosecutors his roommate Tyler Clementi killed himself days after learning about the spying. The suicide touched off a national conversation about bullying of young gays.
