국내 미등록 특허권 사용료와 한미조세협약상 국내원천소득 - 대법원 2025. 9. 18. 선고 2021두59908 전원합의체 판결의 의미와 향후 과제 -

This paper analyzes Supreme Court En Banc Decision 2021Du59908 decided Sep. 18, 2025 (hereafter “the Decision”), and examines whether Korea can exercise its taxing rights over royalties paid by a domestic corporation to a U.S. corporation for the use of patents not registered in Korea, by treating such royalties as Korean-source income. Previous precedents had held that royalties is sourced where the patent is registered based on the territorial principle of patent law. Accordingly, it concluded that royalties derived from patents not registered in Korea do not constitute Korean-source income under the Korea–U.S. Tax Treaty(hereafter “the Treaty”). However, the Decision held that since the term “use” of a patent is not defined in the Treaty, its meaning can be interpreted by applying the proviso of Article 93(8) of the former Korean Corporate Tax Act, that is the laws of the Contracting state whose tax is being determined, pursuant to Article 2(2), first sentence of the Treaty, and that there is no context to exclude such interpretation. On this premise, the Court ruled that if the patented technology is used within Korea, the corresponding royalty income constitutes Korean-source income, thereby overturning a 33-year-old precedent. This paper analyzes the interpretation of undefined terms in tax treaties under domestic law, the scope of “context” that may preclude such interpretation, and the source rule for royalties. It also reviews previous case law and related academic discussions. Building on this analysis, this paper argues that the majority opinion’s interpretation aligns with the principles of tax treaty interpretation and the “place of use” principle adopted in the Treaty, while critically examining the limitations of the dissenting opinion. In addition, the paper discusses remaining issues following the Decision, including the allocation of the burden of proof when domestic source income and foreign source income are mixed, and the interpretation of the 2019 amendment to the Corporate Tax Act.