The school announced the decision with a release on its athletic department website.
Smith (6-foot-5, 335 pounds) was the Nittany Lions' left tackle for the past three seasons and graduated earlier this month with a degree in criminology.
"After achieving one of my life goals of receiving a degree from The Pennsylvania State University, I feel it's time to continue the pursuit of my dream of becoming a NFL player," Smith said in a prepared statement.
Smith has the size, bulk and aggressiveness needed for the next level, but the decision was a surprise because he has been far from dominant. Penn State struggled to run this season, and quarterback Christian Hackenberg frequently was under siege. While the lack of a true feature back hurt, what hurt more was that the offensive line created little push.
While Smith looks to have a good upside, he is not consistent with his technique and had issues in pass protection this season. His workouts will be even more vital than usual when it comes to his draft status; his game tape from this season will not be consistently impressive. At this point, he looks to be a third-day pick.