The 20-year old defender joined Jack Wilshere, Alex Oxlade-Chamberlain, Kieran Gibbs and Aaron Ramsey in committing themselves to the Gunners and he was delighted to be pledging his future to the club.
"Obviously I'm over the moon - really happy," he told Arsenal's official website.
"I see my future at this football club and I'm delighted they see things the same way.
"Signing the contract shows commitment from me, which Arsenal can always count on, but it's a big commitment from them as well.
"People here clearly have belief in me, and now I have to make sure I prove them right."