The Prep lead was only four at the half, but the Griffins beat Sherman 39-27 in the second half.
Cameron Myles added 13 points for University Prep while Brandon Hunt and Devin Green had 10 apiece.
Andrew Graham led Sherman with 17 points.
University Prep next plays in the state semifinals Friday morning at 10am against Martin Luther King from Section 1. The game will be played at the Glens Falls Civic Center.