The present disclosure includes but is not limited to the III-Nitride semiconductor devices including a barrier layer, a gallium nitride or indium gallium nitride channel layer having a Ga-face coupled with the barrier layer, and a patterned thermoconductive layer having a thermal conductivity of at least 500 W/(m-K) within 1000 nanometers of a Ga-face of the gallium nitride channel layer. The semiconductor device may be a high-electron-mobility transistor or a semiconductor wafer. Methods for making the same also are described.