The heat dissipating performance of high-power laser diodes packaged by silicon carbide (SiC) ceramic submounts is investigated, comparing with the commonly-used aluminum nitride (AlN) ceramic submounts. The thermal resistance of SiC and AlN submounts packaged F-mount devices are measured by the thermal resistance instrument based on the structure function method. The thermal resistance of SiC devices is about 3.0 ℃·W-1, and the AlN ones is about 3.4 ℃·W-1. The measured thermal resistance of SiC devices is about 14.7% less than that of the AlN. The experimental data shows better heat-dissipating performance of SiC submounts. In addition, the output characteristics of devices packaged by two kinds of submounts are further tested. The output power of 915 nm single emitter of SiC device achieves 15.9 W at the continuous injection of 16 A, while for AlN device, the value is only 15 W. Test results demonstrate that the SiC packaged laser diode achieves higher power output.