Andreas Christensen has signed a new long-term contract with Chelsea that runs until June 2022, the Premier League champions have announced.
The Denmark international has been rewarded for a season that has seen him start 13 of Chelsea's 22 Premier League matches and displace David Luiz as Antonio Conte's first choice in the centre of defence.
"It feels really good to sign a new contract and I'm just happy to be committed to Chelsea for the future," Christensen told the club's website. "I've played a lot of games, I'm enjoying it at the club and everything is working well."
Club director Marina Granovskaia added: "This contract is reward for the excellent form Andreas has shown in the first half of the season. He showed immense potential when he signed for Chelsea in 2012 and is now enjoying the benefits of the dedication and professionalism he has shown since.
"After two seasons on loan in Germany we were convinced he was ready to be a part of the squad this season and he has grasped the opportunity with both hands. We are delighted he has chosen to commit his future to Chelsea and we look forward to four-and-a-half more successful years with Andreas at the club."
Christensen, 21, joined Chelsea's academy from Brondby in 2012 and won the UEFA Youth League and FA Youth Cup before joining Borussia Monchengladbach on a two-year loan, playing regularly in the Bundesliga and Champions League and being voted the club's Player of the Year for 2016-17.
Chelsea brought Christensen into their first-team squad last summer despite Gladbach's interest in signing him permanently, and the Denmark international has exceeded expectations by forcing his way into Conte's strongest XI with a series of assured performances in defence.
In an interview with talkSPORT in December, former Chelsea technical director Michael Emenalo said of Christensen: "The thing I can tell you is Andreas Christensen, with his technical qualities, his personality, his desire, his love for the club... he is a potential great. I don't know how else to put it, but he is a wonderful, wonderful player. We are all thrilled."