Thornton has been captaining the Sharks for a few years.
Joe Thornton and the San Jose Sharks have reached an agreement on a new three-year $21 million extension.
Thornton is making $7.2 million this year in the final year of his current contract.
“Joe stepped up and made a tremendous commitment to this franchise, his teammates and the fans in San Jose,” Sharks general manager Doug Wilson said. “We are very pleased that we now have another key piece of this team’s core under contract for the next four seasons.”