Police said they are investigating the 22-year-old's death as a possible drug overdose. No arrests have been made.
Smith, a native of Elmira, Oregon, played left tackle and made 36 straight starts over the past three seasons. He was selected to the All-Big Sky second team as a junior last year, when the Vikings finished 9-3 and qualified for the FCS playoffs for only the second time.
"I feel we have the most united, close-knit football team in America, and we just lost a major piece of that team in Kyle," Vikings coach Bruce Barnum said. "Right now we have two concerns, Kyle's family and our football players. The program is being tested, but we will come out of this on top."
The team's Thursday morning practice was canceled.
Smith is survived by his parents, Matt and Angela Smith, a brother, Cody, and a sister, Julia.
Another Portland State player, linebacker AJ Schlatter, died in January after complications from tonsil surgery.