Rivers has been with the franchise since 2004 and this season has led the side to a 4-4 record in the AFC West.
Simms told Chargers.com: "Rivers has been fun to watch. Knowing him all these years, Rivers was born for this offense. To see him do something different and adept this way, it's really what he was made to do.
"He's a high energy guy who likes being in control. This is going to prolong his career and he's going to be a really good player the rest of his career."
Rivers has passed for 2,473-yards so far this year, with 17 touchdowns to his name from his eight appearances.