With the development of Industry 4.0 and the rapid changes in the internal/external environment, it is necessary to have common platform and language for communication and co-work. OPC-UA (Open Platform Communications Unified Architecture) is a platform-independent protocol that allows communication between different hardware/software systems. OPC-UA uses a client-server architecture, where a client can communicate with one or more servers to access data or perform operations. However, the application of OPC-UA is domain-related. To construct an OPC-UA protocol platform for industrial communications requires domain and OPC-UA experts to apply the domain Companion Specifications of OPC-UA. The integration of various domain companion specifications may become a problem when the project includes various domains. By applying ontology to specify the elements of OPC-UA, this research standardizes OPC-UA. The standardized ontological OPC-UA is more readable, adaptable, and transferable. To demonstrate the advantages of ontological OPC-UA, this research applied it to a semiconductor cleanroom monitoring system. The results show the quick adaptability and expandability of the ontological OPC-UA.