ABSTRACT This study explores semantic relevance between internally-headed relative clauses (RCs) and main clauses in Korean, and argues that semantic relevance is caused by the encoding strategy of an internally-headed RC, which is shared by perception-verb complements. An internally-headed RC is distinguished from a gap RC in that the head noun appears in the RC as a full noun. Previous studies have argued that, along with the difference in the position of the head noun, semantic relevance is also required for an internally-headed RC. After showing that descriptions of semantic relevance in previous studies have explanatory limitations, we re-examine semantic relevance by focusing on the encoding strategy of internally-headed RCs, which is shared by complement clauses. The findings show that semantic relevance is required for internally-headed RCs that formally resemble perception-verb complements. After defining semantic relevance as describing a temporary state and as representing causal, temporal and concessive meanings, we explain the former with a perception requirement and the latter with a ‘perception–reaction’ relation between an internally-headed RC and a main clause.