Utilizing a heterogeneous multiprocessor system has become a popular design paradigm to build an embedded system at a cheap cost. A reliability issue, which is vulnerability to soft errors, has not been taken into account in the conventional IC (integrated circuit) design flow, while chip area, performance, and power consumption have been done. This paper presents a system design paradigm in which a heterogeneous multiprocessor system is synthesized and its chip area is minimized under real-time and reliability constraints. First we define an SEU vulnerability factor as a vulnerability measure for computer systems so that we evaluate task-wise reliability over various processor structures. Next we build a mixed integer linear programming (MILP) model for minimizing the chip area of a heterogeneous multiprocessor system under real-time and SEU vulnerability constraints. Finally, we show several experimental results on our synthesis approach. Experimental results show that our design paradigm has achieved automatic generation of cost-competitive and reliable heterogeneous multiprocessor systems.