A study of the noun incorporation phenomenon in Korean suggests that noun incorporation occurs at D-structure and obeys the Head Movement Constraint syntactically, and the Theme-Only Constraint semantically. First, the structure of "sunrise"-type words is identified, showing that before derivation through nominalization of the affix "-i," compounding between the forms for "sun" and "to rise" should occur in the syntax. This fact is then used as direct evidence of noun incorporation, which is a word formation process in the syntax. Based on the structure identified, it is shown that every noun that goes through noun incorporation in the syntax must have the thematic role of "Theme." This observation is represented by the Theme-Only Constraint. Contains 14 references. (MSE)