We report ultra-high-power performance on npn GaN/InGaN double heterojunction bipolar transistors (DHBTs) that is directly grown on a free-standing (FS) GaN substrate. Measured common-emitter current gain (hfe) reaches 80. A quasi-static I–V measurement shows that JC > 141 kA/cm2 and a power density of 3.05 MW/cm2 can be achieved for DHBTs grown on an FS-GaN substrate. When the temperature is increased to 250 °C, a GaN/InGaN DHBT shows hfe = 43 and the offset voltage is reduced from 0.8 V at the room temperature to 0.3 V. Similarly, the knee voltage is reduced from 5.2 V at room temperature to 2.75 V at 250 °C. In this particular device, breakdown voltage (BVCEO) increases from 90 V at room temperature to 157 V at 250 °C.