NFL Network insider Jason La Canfora cited a league source in reporting the deal is worth slightly more than $18 million, with $8 million guaranteed, making Scifres one of the highest-paid punters in NFL history.
Scifres said he had no intention of testing the free-agent market when his current deal was scheduled to expire at the end of this season.
"For me, it's knowing that I'm going to be here," said Scifres, who joined the Chargers as a fifth-round draft pick in 2003. "I didn't get to that free-agent period, my contract didn't run out. And that's the important thing for us, to keep this team together. This team is capable of so much. Look at this locker room. It has unbelievable things written all over it and I'm just happy to be a part of it still and for the next five years.
"This is the place I started and this is the place I want to finish, and now it's possible."
Scifres has consistently been one of the NFL's best punters and was a Pro Bowl alternate from 2004 to 2009.
While Scifres' gross average was a team-record 46.7 yards last year, he was a victim of the Chargers' poor special teams play. He had four punts blocked and another deflected, helping to drop his net average to 30.8 yards.
After the Chargers missed the playoffs, special teams coach Steve Crosby was fired and replaced by Rich Bisaccia.
"It's a new season, a new group of guys and everybody's upbeat and can't wait," Scifres said. "Coach Bisaccia came in here, and everybody's bought in to what he's trying to do. In the preseason we showed that we have a bunch of guys that are dedicated to making our special teams better, and we get a chance to start Sunday."
The Associated Press contributed to this report.