As the number of available Web services increases there is a growing demand to realize complex business processes by combining and reusing available Web services. The reuse and combination of services results in a composition of Web services that may also involve services provided in the Internet. With semantically described Web services, an automated matchmaking of capabilities can help identify suitable services. To address the need for semantically defined Web services, OWL-S and WSML have been proposed as competing semantic Web service languages. Both proposals are quite low-level and hard to use even for experienced Web service developers. We propose a UML profile for semantic Web services that enables the use of high-level graphical models as an integration platform for semantic Web services. The UML profile provides flexibility as it supports multiple semantic Web service languages. Transformations of both ways between OWL-S and UML are implemented to show that the UML profile is expressive enough to support one of the leading semantic Web service languages.