The jury in Madison, Wisconsin also said the patent, which improves processor efficiency, was valid. The trial will now move on to determine how much Apple owes in damages.
Representatives for the Wisconsin Alumni Research Foundation (WARF) and Apple could not immediately be reached for comment.
WARF sued Apple in January 2014 alleging infringement of its 1998 patent for improving chip efficiency.
Cupertino, California-based Apple denied any infringement and argued the patent is invalid, according to court papers. Apple previously tried to convince the US Patent and Trademark Office to review the patent's validity, but in April the agency rejected the bid.
According to a recent ruling by US District Judge William Conley, who is presiding over the case, Apple could be liable for up to $862.4 million (roughly Rs. 5,614 crores) in damages.
He scheduled the trial to proceed in three phases: liability, damages, and finally, whether Apple infringed the patent willfully, which could lead to enhanced penalties.
WARF used the patent to sue Intel Corp in 2008, but the case was settled the following year on the eve of trial.
The case is Wisconsin Alumni Research Foundation v. Apple Inc in the US District Court for the Western District of Wisconsin, No. 14-cv-62.
© Thomson Reuters 2015