The 23-year-old center had 19 goals and 71 assists for a career-best 90 points last season, placing him third on the Senators.
"We feel that he's a great asset to our organization," Senators general manager John Muckler said. "We're happy to have him aboard."
Spezza was selected second overall by the Senators in the 2001 draft and has spent his entire career with the organization.
While playing for Binghamton of the AHL during the NHL lockout in 2004-05, Spezza led the league in scoring and was the MVP. He didn't slow down this past season when he earned $1.1 million.
Spezza says he was happy to get the contract negotiations over with quickly.
"I think it's great," Spezza said. "It shows the confidence they have in me to get a deal done so soon."
In 179 career NHL games, he has 48 goals and 118 assists for 166 points.