Sportsnet's Elliotte Friedman reports that Hertl's deal comes with an $8.1375 million cap hit and a three-year no-movement clause which switches to a no-trade clause for the final five years.
"Tomas has evolved into a premier top-line centreman in the league, competing against the NHL's best players every single night and delivering significant results," Assistant General Manager Joe Will said in a media release. "There are few centremen in the NHL with his combination of physical and dynamic play and he is a player that you build a franchise around. We are fortunate to have two of the league's top centremen on one team with Tomas and Logan Couture.
"By agreeing to this contract, Tomas is cementing his path with the Sharks, following in the footsteps of some incredible players who have worn the Sharks crest. He has shown that he wants to play in San Jose for years to come and it shows his dedication to the organization and community since he joined the team in 2012. We are thrilled to have Tomas for another eight years."
Hertl was one of the top names who could have been available at the NHL trade deadline as he was a pending unrestricted free agent. In 59 games this season, Hertl has 25 goals and 48 points.
The 28-year-old is in the ninth season with the Sharks, who drafted Hertl with the 17th overall pick in the 2012 NHL Draft.
In 562 career games, the Czech forward has 176 goals and 371 points.