In recent years, we witnessed a sharp increase of online social networks (OSNs) such as Twitter, Facebook and MySpace just to name a few. In these cyber spaces, one can set up a profile about oneself, invite friends to join the site and link these people together with the purpose of sharing information and resources. However, the user faces many prob- lems related to trust. This kind of problems grasped the attention of the researchers about the importance of managing trust in OSNs. However, how to store relevant information related to trust, while offering the ac- cess to it to the OSNs' users, is rarely discussed in the literature. To address some of the current limitations, we introduce a novel approach that exploits the Semantic Web and especially the FOAF ontology. In fact, using the semantics of the FOAF ontology and applying Seman- tic Web reasoning techniques, we show that trust relationships can be merged between different users from multiple social networks