Advances in FPGA technologies allow designing highly complex systems using on-chip FPGA resources and intellectual property (IP) cores. Furthermore, it is possible to build multiprocessor systems using hard-core or soft-core processors, increasing the range of applications that can be implemented on an FPGA. In this paper we propose a symmetric multiprocessor architecture using the Microblace soft-core processor, and the operating system support needed for running multithreaded applications. Four systems with different shared memory configurations have been implemented on FPGA and tested with parallel applications to show its performance.