Due to either the inherent complexity of the domain or the evolving nature of systems, we can envision solutions that digitalize assets in a complex domain using an ecosystem of distributed Digital Twins instead of a single monolithic one. To effectively tackle interoperability in such ecosystems, this paper advocates for the introduction of a representation based on Semantic Web technologies enabling the discovery of both Digital Twin structure – i.e. the static information about the asset model and offered services – and state – i.e. the data and metrics collected at runtime – to support the management of ecosystems and the creation of application mashups. A review of the state of the art suggests that currently investigated ways to describe a Digital Twin are not sufficient to achieve this objective and a proposal of key requirements and their implementation using Semantic Web technologies is outlined.