This paper introduces semantic reflection, a novel concept for a modular design of intelligent applications. SCIVE, a simulation core for intelligent Virtual Environments (IVEs), provides semantic reflection on multiple layers: SCIVE’s architecture grants semantic driven uniform access to low-level simulation core logic, to specific simulation modules’ application definitions, as well as to high-level semantic environment descriptions. It additionally provides a frame to conveniently interconnect various simulation modules, e.g., for graphics, physics, audio, haptics, or AI etc. SCIVE’s Knowledge Representation Layer’s base formalism provides the central organizing structure for the diverse modules’ data representations. It allows bidirectional knowledge driven access between the modules since their specific data structures and functions are transitively reflected by the semantic layer. Hence SCIVE preserves, integrates and provides unified access to the development paradigms of the interconnected modules, e.g., scene graph metaphors or field route concepts etc. well known from todays Virtual Reality systems. SCIVE’s semantic reflection implementation details are illustrated following a complex example application. We illustrate how semantic reflection and modularity support extensibility and maintainability of VR applications, potential for automatic system configuration and optimization, as well as the base for comprehensive knowledge driven access for IVEs.