The aim of the paper is to evaluate the adequacy of noise spectroscopy to significantly improve the selectivity of microsensors compared to a conventional acquisition of the sensor resistance variation. Significant results of low frequency noise characterization of metal-oxide gas microsensors with WO3 sensitive thin film are presented. Using developed measurement system, noise spectra show a clear Lorentzian behavior for all tested gases according to adsorption-desorption noise theory. To identify the detected gas, a physical-based characterization model of adsorption-desorption noise source is proposed and compared with the empirical flicker noise model. We show that the excess noise is due to the adsorption-desorption processes on the surface of the sensors sensitive film. The Lorentzian parameters depend on the nature of the gases and the noise level dependence with gas concentration is clearly demonstrated. The most relevant result of our study is the largest dynamic range of noise levels variation relative to sensor resistance variation. Our results confirm the growing interest in the development of noise spectroscopy technique to improve the selectivity of gas sensors.