We demonstrated the impedance spectroscopic characterization of ammonia gas sensors based on the drop-deposited, 99% semiconductor-enriched SWCNT networks, over a range of frequencies (0.5 Hz to 300 kHz) and NH3 concentrations (3.6–41.4 ppm). The experimental data were fit with an equivalent electrical circuit consisting of one resistor and two subcircuits containing a resistance and constant phase AP20187 in parallel, and values of the circuit parameters were obtained from the fitting process. The 99% semiconductor-enriched devices were found to exhibit a complex impedance and have a sensitivity in the impedancemetric operation mode of approximately twice that of a direct current measurement. Furthermore, in contrast to the dc measurement, the impedance spectroscopic data clearly revealed the role of the absorbed gas molecules for the performance of highly enriched SWCNT network gas sensors and the underlying sensing mechanisms. Impedancemetric operation showed the potential to overcome the drawbacks of conventional direct current measurement, including higher sensitivity to NH3 and better stability due to subtracting out undesirable contributions in the very low frequency. Therefore, we believe that the impedance spectroscopy method could be a powerful tool for investigating the performance of highly semiconductor-enriched SWCNT gas sensors and for further developing the nano-sized semiconducting gas sensors.