In this paper, an L-band GaN-based power amplifier on SiC substrate with kilowatt output power is presented. The experimental DC breakdown voltage and maximum output current can reach 250 V and 0.52 A/mm, respectively. Then, we demonstrate a GaN-based HEMT exhibiting a maximum output power of up to 1003W (20.06 W/mm), an operating voltage of up to 100 V, a power-added efficiency (PAE) of 76%, and an associated power gain of 17.1 dB at 1.3 GHz. It was experimentally found that the DC drain current components from the output power all fall on the same curve independent of operation drain voltages. Finally, a theoretical discussion of the influence of the DC drain current component on the output power is briefly given.