Nowadays, many health centers use Hospital Information Systems (HIS) for the daily management of center activities such as patient data management. In Burkina Faso, many HIS are used for patient data management but these systems cannot cooperate because the data sources are often heterogeneous. In order to guarantee a better diagnosis in patient management, physicians need to access these data sources in a unique way through queries. For better analysis of a patient's situation, the health worker may want to access multiple data sources that do not belong to the same health center. This is only possible if the HIS involved interoperate. In a previous work, we proposed an interoperability architecture based on semantic web services. This solution has the advantage of not modifying the current organization of health centers. Indeed, for a complex query, a composition of web services is a solution to satisfy different needs. In this paper, we detail our approach for composing semantic web services. In our approach, the functionalities of each HIS application will be implemented by a web service semantically annotated by an ontology. An ontology-based mediation service is used to enrich the physician query and the MiniCon algorithm to create a composite web service. The composite web service is executed to return the requested data.