In September 2019, he moved to Slaven Belupo in Croatia, but left the club two months later.
[2] He moved back to South Korea to join Ulsan Hyundai FC ahead of the 2020 K League 1 season.
In his first season with Ulsan, he helped them win the 2020 AFC Champions League for the second time in the club's history.
[3] On 23 May 2011, Koh was called up to the South Korea national team for the friendly matches against Serbia and Ghana, though he did not play.
[4] He made his national team debut in a friendly match against Australia on 14 November 2012 in a 2–1 loss.