In article number 1800159, Young Min Song, Jizhou Song, Kyung-In Jang, and co-workers develop a bio-integrated optoelectronic device with integration of thin metallic heat sink for interfacial thermal management. It exhibits excellent heat dissipation capabilities for thermally safe long-term usability, due to the high thermal conductivity and film-type geometrical design of the heat sink for skin applications. The architecture of the device with the metallic heat sink ensures mechanically and thermally invisible blood flow monitoring.