Arsenal had been interested in signing Dembele when the transfer window re-opens in January.
However, Portuguese believes the 21-year-old attacker doesn't see his short-term future away from the Catalan club.
Semedo told ESPN: 'He is an excellent player, with a lot of potential and will help us a lot. He is totally committed to the team. Now he is more responsible and is showing it in the field. It must continue like this, and I am convinced that it will.
He has scored seven times his term as Barcelona have again demonstrated their dominance at the top of La Liga".