The midfielder, 19, only joined Spurs from MK Dons last year.
But Spurs have moved to reward the England international for an impressive start to his White Hart Lane career with a pay rise.
"We're delighted to announce that @Dele_Alli has signed a new contract with the club which will run until 2021," read a statement on Spurs' official Twitter account.
Alli boasts 30 appearances for club and country this season and has hit goalscoring form of late, netting five times since November.
He cost Spurs £5million when they signed him from MK Dons at the end of last winter's transfer window and was immediately loaned back to his boyhood club for the rest of the season.
Spurs are thought to have given Alli a pay rise from the £10,000-a-week deal he originally signed last February.