The Gunners signed the Chile international from Barcelona for £32m, and he has scored eight goals in 15 appearances in all competitions so far this season.
Former Manchester United forward Yorke told Sky Sports News: "Arsenal and everyone who has watched world football saw what he was doing at Barcelona before he joined the club.
"He's delivering week in week out. He's really risen the occasion and he's come in to a new environment and he's quickly adapted to being an Arsenal player.
"He's been outstanding. He's that type of player with his fantastic skill and ability to play for the team, but he's also getting in on the goals and that's eight so far this season. That's a terrific return."
Sanchez scored both goals in Arsenal's 2-0 Premier League win over Sunderland on Saturday.