This document describes techniques and apparatuses that implement a high thermal conductivity region for optoelectronic devices. In some embodiments, a printed circuit board (PCB) includes a high thermal conductivity region that extends through the PCB. The high thermal conductivity region has first and second surfaces that are approximately coplanar with exterior layers of the PCB. A side-emitting optoelectronic device is mounted to the first surface of the high thermal conductivity region via conductive material that enables conduction of the device's heat into the high thermal conductivity region. The high thermal conductivity region can then transfer the heat away from the device and toward the second surface of the high thermal conductivity region, thereby improving the device's thermal performance.