The 21-year-old left-back has made 19 appearances in the league this season, with 17 of those being starts.
Sporting director Jochen Saier sees Gunter as an exciting prospect for the future and is delighted to have agreed a new deal with the player.
"Christian Gunter has made great development and improved (this season)," Saier told the club's official website.
"It has been gained not least because of his professional attitude and good mentality. We look forward to continuing to work with Christian."
Gunter also expressed his satisfaction, having graduated from Freiburg's reserve team.
He said: "The way Freiburg have accompanied me in my footballing education is excellent.
"I have a lot in common with the club and I am very excited about the early contract extension."
Freiburg currently sit second-bottom of the Bundesliga, having won only four games this term, but are only one point from safety.
