Feature models are widely used in domain engineering to capture common and variant concepts among systems in a particular domain. However, the lack of a formal semantics of feature models has hindered the development of this area. This paper presents a Semantic Web environment for modeling and verifying feature diagrams using ontologies. We use OWL DL (a decidable di- alect of OWL) to precisely capture the relationships among features in feature diagrams and configurations. OWL reasoning engines such as RACER are de- ployed to check for the inconsistencies of feature configurations fully automati- cally. As part of the environment, we also develop a CASE tool to facilitate the visual development, interchange and reasoning of feature diagrams represented as ontologies.