The 19 year old defender, who was linked with a summer move to Huddersfield, has signed a one year contract extension with the Wearside outfit.
He had a controversial season in the Premiership. Arsene Wenger was outraged as a Dan Smith lunge put Abou Diaby's career in doubt.
Smith told the club website: "We have been in talks over the summer and it was agreed when I was on holiday.
"I have now got to push on and try to get in the starting XI, or at least be in the squad every week."