A semantic framework to improve automated reasoning, retrieval, reuse and communication of engineering design knowledge is presented in this research. We consider design to be a process involving a sequence of decisions informed by the current state of information. As such, the information model developed is structured to reflect the conceptualizations of engineering design decisions with a particular emphasis on semantically capturing design rationale. Based on a description logic formalism, the information model was implemented using the Web Ontology Language (OWL), which provides a semantically rich and sufficiently broad specification of design decisions capable of supporting the application of any specific decision-making method. Through this approach knowledge reuse is achieved by communicating design rationale and facilitating semantic-based retrieval of knowledge. A case study is presented to illustrate three key features of the approach: 1) seamless integration of separate modular domain ontologies and instance knowledge related to engineering design that are needed to support decision making, 2) the explicit documentation of design rationale through design decisions, and 3) the application of an automated method for matching and retrieving stored knowledge. The automated retrieval method is implemented using the Semantic Web Rule Language (SWRL) and serves as an example of the type of reasoning services that can easily be achieved by formally and semantically representing design knowledge.