Overview: Digital Twins require semantically consistent integration of information about equipment, physical connections, and time series. A semantic layer based on ontological definitions and knowledge graphs can provide a consistent representation of domain knowledge, enabling applications to better understand relationships between assets and data and retrieve the right information in less time. Our preliminary results are: (i) the definition of a semantic layer based on ontologies for equipment, physical connections, and time series; (ii) the use of knowledge graphs to contextualize and connect heterogeneous information; (iii) initial ideas on how semantic technologies can support more intelligent applications and improve information retrieval in Digital Twin environments.