Ki had a year left on his old deal after arriving from Celtic for what was then a club record £5million in 2012
"I'm very pleased," Ki told the club's official website
" This is what I have wanted to do - my first option was always to renew with Swansea
" I want to sacrifice myself for the team and, as always, do as much as I can to help this team improve
"I will be giving 100 per cent, and I am looking forward to continuing my work with the club."
Ki's new deal represents a remarkable turnaround in his fortunes in South Wales
Despite making 38 appearances in his first season at Swansea - which included a Capital One Cup win at Wembley - Ki was loaned out to Sunderland for the 2013-14 campaign, helping the Black Cats to a League Cup final appearance as well as winning their battle against relegation
Sunderland and Aston Villa were both keen on securing Ki's services on a permanent basis but the 25-year-old has once more established himself under Liberty boss Garry Monk
Ki scored his first goal for the club in Swansea's opening-day victory over Manchester United at Old Trafford and has been impressive as Monk's men have won their first two Premier League games
"This team has a great potential, and I am sure that we will be amazing as time goes by," said Ki
"The way we try to play makes it really enjoyable
Hopefully we can win more trophies.
"It was amazing to be at Wembley for two years in a row, and it would be massive if I could return again this year."
Source : PA
Source: PA