Research on the relationship between R&D investment and firm performance has produced conflicting results—positive relationships, no relationships, or negative relationships—adding to the confusion. In this context, recent calls have emphasized the need for research on the linking mechanisms through which R&D investment specifically affects firm performance, and in particular, many arguments have been raised that technology management capability is critical for the two factors to have a close relationship. Accordingly, the primary purpose of this study is to add technology management capability as a process variable between R&D investment level and firm performance, and to conduct an in-depth examination of the relationships among R&D investment, technology management capability, and firm performance. Using a sample of 175 Korean firms possessing R&D laboratories and employing structural equation modeling for empirical analysis, the results showed that technology management capability moderates the relationship between R&D investment and firm performance. Additionally, a significant negative relationship was found between R&D investment level and firm performance. These results imply that strengthening technology management capability is more important than simply increasing R&D investment to enhance firm performance. In particular, continuously increasing R&D investment in the absence of adequate technology management capability is akin to "pouring water into a bottomless jar," potentially resulting in significant waste of critical managerial resources and ultimately posing a serious threat to the firm's survival and growth. Therefore, this study clearly demonstrates that to effectively link R&D investment to firm performance, firms must go beyond merely increasing R&D investment and actively strive to level up their technology management capabilities as embodied in technology strategy, technology processes, technology organization, and technology leadership.