It happened around 3:15 p.m. along Route 126 and Schlapp Road near Oswego.
State police say it appears the driver of the car, Brian Herrera, 19, of Plainfield, pulled out in front of the semi. That's when the truck slammed into the vehicle.
Herrera and two passengers in the car Alexis Banuelos, 18, and Tyler Montgomery, 19, all died. The truck driver suffered minor injuries.
"It is the most unsafe intersection I have ever seen in my life," said Sandy Diller, neighbor. "At least once a month, there is a wreck at that corner."
The crash is under investigation.