This study tests the complexity hypothesis that syntactic structures involving a more complex representation impose a greater processing load. I show that Korean psych verbs that exhibit a three-way structural distinction (Belletti & Rizzi 1988) differ in the syntactic and semantic complexity. In particular, the causative object Experiencer construction is associated with more structure and complex semantics, compared with the two types of subject Experiencer constructions. Experiment 1 demonstrates that the more complicated causative psych verb group incurs a higher processing cost. In Experiment 2, it is revealed that the causative configuration is less likely to be used when speakers have access to simpler structural options. The results of the present study on Korean psych verbs imply that the complexity hypothesis is functional at both comprehension and production levels. Comparisons and contrasts with English psych verb studies are discussed. Finally, some alternative accounts are considered and refuted.