Financial terms were not released.
The 27-year-old defenseman, who could have become an unrestricted free agent on July 1, has nine points (two goals, seven assists) in 47 games this season, and 18 points (three goals, 15 assists) in 88 NHL games since signing with San Jose as a free agent on May 23, 2017.
"Radim has been an integral piece of our team defense for the last two seasons," Sharks general manager Doug Wilson said. "His style of play blends a sound defensive game, coupled with a heavy physical ingredient and good puck-moving skills. His impact on our club when he is in the lineup is undeniable, and we're pleased he will be part of our team's core moving forward."
The Sharks (29-35-5) have lost three straight games (0-2-1) and are 14th in the Western Conference, ahead of only the Los Angeles Kings.
