The teenager has been on fine form in the second half of this season, helping the Gunners to back-to-back wins in the Premier league.
The youngster signed a deal worth up to to £10,000-a-week, last October. That agreement was due to run until 2019.
And since then he has made significant improvement in his game, breaking into the first team for the first time since the turn of the year, and boss Arsene Wenger was keen to reward the academy product with improved terms.
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He has started four of the last five games and followed up his first goal against Everton before the international break with another strike against Watford on Saturday.