Six Sigma implementation is for the quality and productivity improvement in manufacturing areas as well as the process improvement of entire management, by the activities of management innovation aiming for obtaining companies` profitability and encouraging competitiveness. As a result of analyzing the critical factors of successful Six Sigma companies which implemented Six Sigma in relation to electronic industry by small and medium sized companies as well as big companies, we could find the difference of success factors between small and medium sized companies and big companies. The critical success factors of big companies are followings; CEO`s transformative leadership, computer system construction, supportive infrastructure including incentive system. In case of d and medium sized companies, the critical success factors are measured by CEO`s transformative leadership, Black Belt system, expect from supportive infrastructure. Also, the research result showed that there were the differences between strategic implementation scopes and critical factors in implementing steps, by the perspectives of key leaders.