In this paper we discuss the noun incorporation phenomenon based on the data from Korean. We show that noun incorporation of Korean occurs at D-structure and obeys the Head Movement Constraint (HMC) by Travis (1984) and Chomsky (1986) syntactically and the Theme-Only Constraint semantically. For the discussion, we first identify the structure of ‘hæ-tot-i’ sunrise- type words, and show that before derivation, through attachment of the nominalizing affix ‘-i’, compounding between ‘hæ’sun and ‘tot’ to rise should occur in syntax. This observation is used as direct evidence for noun incorporation which is a word formation process in syntax. Based on the structure identified, we show that every noun which goes through noun incorporation in syntax should possess the thematic role of Theme . This observation is captured by the Theme-Only Constraint.