West Brom chief Ashworth delighted with Foster business
He was named Albion's supporters' player of the Year and players' Player of the Year and kept 10 clean sheets, equalling the club record for the most shut-outs in a Premier League campaign.
Baggies sporting and technical director Dan Ashworth said: "The players, the staff and supporters will be delighted Ben has agreed to join us permanently.
"Ben showed to everyone last season how important he is to us, making vital saves at key moments in games.
"He was happy here, enjoyed the goalkeeper coaching under Dean Kiely, the facilities, the supporters, and everything about the club."