ABSTRACT We developed High Level Synthesis System which synthesizes a Register Transfer (RT) level circuit from an LSI behavior specification described in the Pascal language. We prove that the parallel Simulated Annealing with heuristic knowledge can offer speed-up in solving Combinatorial Optimization Problems. Key Features Rule-based Annealing(RA) RA generates the new configuration not only at random but also through heuristic knowledge (rules). By letting rule selection ratios change dynami- cally according to the cost reduction ratio of each rule, a better solution is produced at the appointed optimization time. Parallel formulation of RA PEs are clustered based on acceptance ratios. PEs in one cluster opti- mize one configuration co-operatively and let the acceptance ratio increase at medium and low temperatures.