This paper presents novel pulse width modulation circuit for fast transient response. In the proposed modulator, C-MOS logic inverters are used instead of high speed comparators. Four types of new modulator are proposed and operating principle described in detail. The proposed modulator is applied to a buck converter, and steady state characteristics and frequency response of the proposed modulator are measured with the bread board circuit. From the experimental result, it is found that the proposed modulator has the derivative characteristics as hysteretic PWM controller that has good transient performance. Excellent load and line regulation are obtained. By using C-MOS inverter, compared with conventional hysteretic PWM controller with fast comparator, cost is reduced to one-fifth.