The new deal will keep the former PSV Eindhoven star at Old Trafford at least until the summer of 2013.
"I have enjoyed every minute of my time at United," the 30-year-old told the club's official website.
"I'm delighted to be part of the club during this latest stage in its history - with another exciting young team being built.
"I'm looking forward to playing my part in keeping United at the top of the game."
United boss Ferguson added: "Ji has been an important player for us for a number of years now.
"He has great ability and energy and in recent seasons has added the knack of scoring important goals in big games.
"He is a popular member of the squad and his experience at domestic and international level is invaluable for the younger players."