We report a normally-off GaN-based transistor using conductivity modulation, which we call GIT (Gate Injection Transistor). This new device principle utilizes hole-injection from p-AlGaN to AlGaN/GaN heterojunction, which increases electron density in the depleted channel resulting in dramatic increase of the drain current owing to the conductivity modulation. The fabricated GIT exhibits the threshold voltage of 1.0V with high maximum drain current of 200mA/mm. The obtained on-state resistance (Ron·A) and off-state breakdown voltage (BVds) are 2.6mΩ·cm 2 and 640V, respectively. These values are the best ones ever reported for GaN-based normally-off transistors.