The former Germany Under-21 international's previous deal was due to expire at the end of next season, but the 23-year-old has committed his future to the club until June 2018.
Jantschke progressed from Gladbach's academy and has established himself as a first-team regular at Borussia-Park.
The right-back has started all but one Bundesliga game for Lucien Favre's side this season as they strive to qualify for Europe next season.
News of Jantschke's agreement comes just a day after club captain Filip Daems signed a new one-year deal with the club.
Gladbach host Hoffenheim on Saturday having taken just one point from four league matches following the mid-season break.
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