We investigate the H2S sensing characteristics of the amplifier circuit consisting of the pFET- and resistor-type gas sensor. The pFET- and resistor-type gas sensors are fabricated on the same substrate. When exposed to H2S gas, the drain current of the pFET-type gas sensor decreases while the current of the resistor-type gas sensor increases. The Vout of the amplifier circuit changes more sensitively to gas molecules than that of other amplifier circuits since the pFET-type sensor has complementary sensing characteristics to the resistor-type sensor.