The importance of service industry in national economy is getting increasing due to current trend of aging society and increasingly desire for better quality of life. However, the level of labor productivity in domestic service industry is lower than Japan and Germany that are typically strong in manufacturing industry. Difficulty of process control and measurement in accordance with variability and intangibility which are features of service industry, is considered as the cause of this poor labor productivity in Korea. This study aims to present managerial implications by calculating sigma levels on branch bank service quality and suggesting the quality dimensions of banks can be checked through a gap comparison between the sigma level on service quality in the whole banks and service quality in each bank. Quality level presented by the KS-SQI is applied to the measurement method that Yoo Han Joo and Song Kwang Seok suggested in 2006. Spss18.0 is used as an analysis tool. As a result of factorial analysis, 7 dimensions of service quality in KS-SQI can be divided into new 3 dimensions of service quality. This study also suggests that width and number of questions in previous questionnaire shall be extended. The whole of the bank service quality level is evaluated 3 sigma. The research help banks to figure out their service quality level through gap comparison objectively.