This paper proposes a 600- V half-bridge GaN active gate driver with built-in dV/dt self-adaptive control utilizing a common-mode (CM) noise sensing and amplifying unit. The two 600- V LDMOS FETs existing in the conventional level shifter are used to sense the CM noises. When the dV/ dt rate is large enough, the sensed CM noises will be amplified and then rapidly provide a pull-down gate current for reducing the turn-on speed. As the dV/dt rate becomes smaller, the pull-down gate current will decrease adaptively, which achieving double peaks in the waveform of driving current. Compared to adding an extra high-voltage capacitor or LDMOS as a dV/dt sensor, this method has no additional area overhead and negligible control delay. At the same slew rate, we compare the low-side gate noises induced by Miller coupling at condition of either only RON or the proposed self-adaptive adjustments. It shows that the noise peak in VGL for self-adaptive control decreases 46% at VJN=300V and also the noise envelope becomes smaller due to the dV/dt adjustment, dramatically reducing the probability of shoot-through current in the half bridge.