A novel gas-sensing system based on a dynamic non-linear response is reported for evaluating the competition effect on the sensor responses to gaseous mixtures. A sinusoidal temperature change is applied to a semiconductor gas sensor; and the resulting conductance of the sensor is analyzed. The sensor response changes characteristically depending on the composition of the gaseous mixtures and is analyzed by fast Fourier transformation (FFT). Not only the individual concentrations of the samples but also the competition effect on the sensor responses to the gaseous mixtures are evaluated by the higher harmonics of FFT. The competition effect on the response to two samples is theoretically simulated in relation to the kinetics of gas molecules on the semiconductor surface.