The South Korean Supreme Court issued Decision 2021Du59908 on 18 September 2025 that sets a new precedent on whether royalties paid for patents not registered in South Korea constitute Korean-source income under the 1976 South Korea-U.S. tax treaty. The case arose from a patent infringement dispute that ultimately resulted in the payment of royalties by a Korean company to a U.S. company, on which tax was withheld as per the terms of the treaty. The U.S. company then claimed a refund of the t…