This paper introduces an ontology-based approach to annotating semantics of digital engineering resources. The aim is to enhance design knowledge sharing through semantic annotation to support streamlined collaboration in multidisciplinary consumer product development. Two issues are focused: how to specify the meaning of annotations with design ontology to ensure sharability of the annotation content; and how to represent annotations in neutral encoding formats to seek mutual understanding of the annotated semantics across multidisciplinary design teams and systems. Two use scenarios of semantic annotations in multidisciplinary design of consumer products are illustrated in the paper.