The work is aimed at study of correlation between quasi 1D silicon nanostructures adsorption properties and their electrical characteristics in terms of change in Si nanowires impedance under action of different environments with a target adsorbate. Here we fabricate silicon nanowires based gas sensor and demonstrate the possibility of qualitative and quantitative gaseous media analysis for the presence of ammonia. The equivalent electric circuits of the sensor under action of air, water vapour and water ammonia solutions are considered. The sensor response under action of the different adsorbates and optimal impedance spectroscopy parameters are discussed.