Although gas sensors have been developed previously to achieve high selectivity for a particular chemical species, it is difficult to distinguish chemical species based on static information obtained with a single detector, such as the conductance of a semiconductor. This difficulty is due to the fact that gas sensors usually respond to interfering materials which coexist in a gas sample. In addition, a saturation effect at high concentration, competition among chemical species at the sensor surface, and the accumulation of an aging effect or hysteresis brought about by the use of the sensor for a long period. Recently, we described anew gas-sensing method with which we could quantitatively characterize the dynamic nonlinear responses of a semiconductor gas sensor by sinusoidally varying the power supply to the sensor heater and FFT analysis on the output response. In this paper, we report that the characteristic nonlinear responses to gas species, the saturation effect, and the competition between two gases on the sensor surface is quantitatively evaluated in relation to the kinetics of gas molecules at the sensor surface and the temperature-dependent surface barrier potential.