This study adopted the DEA model to analyze what factors generate inefficiency between inputs and outputs in the production structure of domestic banks' Internet banking operations. For this purpose, the banks under analysis were classified into four characteristic groups: (1) Internet banking early-mover/late-mover banks, (2) Internet banking high-investment/low-investment banks, (3) Internet banking initial concentrated investment/distributed investment banks, and (4) banks with superior/inferior management performance. The results of analyzing each characteristic group from both the customer perspective and the bank perspective are as follows. (1) For the early-mover/late-mover Internet banking banks, the efficiency gap in input-output structure between banks from both customer and bank perspectives was shown to arise through gaps in pure technical efficiency rather than scale efficiency, attributable to first-mover effects. (2) For the high-investment/low-investment Internet banking banks, the efficiency gap in input-output structure between banks from the customer perspective was shown to arise through gaps in pure technical efficiency rather than scale efficiency, attributable to the management investment mindset effect. (3) For the initial concentrated investment/distributed investment Internet banking banks, the efficiency gap in input-output structure between banks from the bank perspective was shown to arise through gaps in pure technical efficiency rather than scale efficiency, attributable to the management investment mindset effect. (4) For banks with superior/inferior management performance, the superiority or inferiority of management performance among banks was found to be difficult to regard as a factor affecting Internet banking efficiency. However, whether these analytical results stem from the fundamental independence of the offline production structure and the Internet banking production structure, or from measurement error in the classification criteria for banks with superior/inferior management performance, requires further research.