Ontology is a knowledge representation formalism used in the Semantic Web to provide data understandable by both humans and computers. The success of the Semantic Web depends strongly on the development of ontologies so that it is considered the heart of the Semantic Web. With the evolution of the Semantic Web recently, ontology is becoming more and more important in the field of knowledge management and sharing. There is an actual demand for fast and easy ontology engineering to save time and effort in ontology construction to avoid the knowledge acquisition bottleneck. Therefore, this paper proposes a semi-automatic approach to ontology construction for Vietnamese high school physics subjects including two steps. The first step is to manually build a “seeding” ontology based on the textbook glossary. Then, a pattern-based method is used to enrich the base ontology to save time and effort. The evaluation result shows that the pattern-based method is suitable for enriching the ontology and provides a good trade-off between simplicity and enrichment result.