Son has emerged as one of Tottenham's key players under manager Mauricio Pochettino.
He played in 53 of their 55 matches last season, scoring 20 goals in all competitions, as Tottenham finished third in the Premier League, reached the FA Cup semi-finals and the Champions League last 16.
The 26-year-old has scored 47 goals in 140 appearances for Tottenham since signing from Bayer Leverkusen in 2015, making him the top Asian scorer in Premier League history.
Son, who also netted twice for South Korea at the World Cup in Russia, has now been rewarded for his fine form with an improved new deal.
"We are delighted to announce that Son Heung-min has signed a new contract with the Club, which will run until 2023," a statement on Tottenham's website said.
Son will join up with Tottenham ahead of their tour of the United States, where they play in the International Champions Cup against Roma, Barcelona and AC Milan.
He will also be available for Tottenham's opening game of the Premier League season at Newcastle on August 11 before travelling to Indonesia to represent South Korea at the Asian Games.