Directional Serial Verb Constructions (Directional SVCs), which are a subset of Serial Verb Constructions (SVCs) in Thai and involve motion-related verbs, are studied in this paper. According to two syntactic tests, two phrase structural schemata are involved in Thai Directional SVCs, including a recursive VP-over-VP structure and a complementation structure. Thai Directional SVCs also exhibit a dissociation between constituent structure and linear order. With this distinctive syntactic structure, Thai Directional SVCs are not reduceable to previously described SVCs. Nevertheless, within Head-Driven Phrase Structure Grammar, the rich featural specifications of heads and the mechanisms available for the percolation of specific head properties in a default interpretation of the Head Feature Principle allow for a straightforward model of Thai Directional SVCs.