The new deal will keep Foster at the club until 2013.
He told the club’s official website: “I’m really happy to commit my future to the club.
“The team spirit here is fantastic and working alongside Edwin and Tomasz (Kuszczak) has been a great influence on my career.”
United boss Sir Alex Ferguson added: “We are delighted that Ben has signed a new four-year deal.
“Ben is seen as one of the best young goalkeepers in England and we genuinely see him as a successor to Edwin Van Der Sar.”
Foster joined United from Stoke in July 2005.