Dual operating modes (DOMs) control technique is presented to achieve fast-transient response for dc-dc buck converter in this brief. The proposed operational transconductance amplifier with DOM control circuit which is used as an error amplifier in the pulse-width modulation (PWM) control circuit. This approach conduces to transient response by accelerating the output level shifting of the error amplifier. Thus, PWM control circuit generates the proper signal to drive the power transistors. Finally, the output voltage of the dc-dc buck converter is rapidly recovered when the load transient occurs. The proposed dc-dc buck converter is fabricated using TSMC 0.35 μm 2P4M CMOS technology. The chip area is 1.38 × 1.45 mm². The operating frequency is set at 1 MHz. The load current range is from 100 to 500 mA. Measurement results demonstrate that the transient recovery time of the proposed dc-dc buck converter with DOM control technique both are 2 μs for step-up and step-down load transient. Comparing with conventional dc-dc buck converter, we find that transient recovery time of proposed dc-dc buck converter with DOM control circuit is improved by over 4.6 and 4.4 times for step-up and step-down load, respectively.