To achieve reliability, reusability and cost reduction, a significant trend of building large, complex real-time systems is to integrate separated application modules. An essential requirement of integrated real-time systems is to guarantee strong partitioning among applications. In this paper, we propose a microkernel, called the SPIRIT (Strongly Partitioned Integrated Real-tIme sysTem) μKernel, for strongly partitioned real-time systems. The SPIRIT-μKernel has been designed and implemented based on a two-level hierarchical scheduling methodology such that the real-time constraints of each application can be guaranteed. It provides a minimal set of kernel functions, such as address management, interrupt/exception dispatching, inter-application communication and application scheduling. To demonstrate the feasibility of the SPIRIT-μKernel, we have ported two different application-level real-time operating systems (RTOSs)-WindRiver's VxWorks and Cygnus's eCos-on the top of the microkernel. The SPIRIT-μKernel architecture is practical and appealing due to its low overheads of kernel services and the support for dependable integration of real-time applications.