With the wide spread of Web services, there is a growing interest in semantic Web services based on ontologies, which support the automated discovery, selection, and composition of Web services. OWL-S is a de facto standard ontology for describing the semantics of Web services. Due to the complexity of the OWL-S grammar, it is difficult to construct OWL-S descriptions manually. This paper presents an efficient model-driven approach to generate OWL-S ontologies from Unified Modeling Language (UML) models, which are widely used for software design and development. The proposed method is based on UML profiles to represent the characteristics of OWL-S. Specifically, a domain ontology is transformed into a class diagram, and UML diagrams are extended to represent the behavior of business processes. Finally, an XML metadata interchange (XMI) file extracted from UML diagrams is transformed into an OWL-S representation via an extensible stylesheet language transformation (XSLT) script. Experimental results with a large number of UML diagrams show that the proposed method handles effectively the control flow of complex processes.