Despite that OLED screen has been increasingly adopted in smartphones to save power; screen is still one of the most energy-consuming modules in smartphones. Techniques such as local dimming are proposed to further reduce the power consumption of OLED screen, but it is hard to decide which part of the screen could be dimmed, and it often results in compromised user experience. Intuitively, when a user interacts with a smartphone via the touch screen, the screen areas are covered by the user’s fingers and even some of the neighboring areas could be safely dimmed. Thus, in this paper, we propose FingerShadow, a new technique which does local dimming for the screen areas covered by user fingers to save more power, without compromising the user visual experience. We have studied 10 users’ touch interaction behaviors and found that on average 11.14% of the screen were covered by fingers. For these 10 users, we estimate that FingerShadow can achieve 5.07%~22.32% power saving, averaging 12.96%, with negligible overhead. We discuss the challenges and future research work to implement FingerShadow in existing smartphone systems.