Rapidly responding, reversible, sensitive, and selective porous silicon-based (PS) gas sensors, operating at low power, are formed with a highly efficient electrical contact to a nanopore covered microporous array. Significant changes in sensor surface sensitivity can be correlated with the strong and weak acid-base (HSAB) character of the interacting gas analyte and the acidic nature of the PS surface so as to produce a dominant physisorption and create a range of highly selective surface coatings. This selection process dictates the application of nanostructured metal oxide and/or nanoparticle catalytic coatings, and provide for notably higher sensitivities which, in concert, form a basis for selectivity. Depositions which include AuxO, SnOx (Sn+2,+4) , CuxO ( Cu+1,+2), NiO(Ni+2) , nano-alumina, and titania, provide for the detection of gases including NO, NO2, CO, NH3, PH3, and H2S in an array-based format at the sub-ppm level. The value of this conductometric sensor technology results from a combination of (1) its sensitivity and short recovery time, (2) its operation at room temperature as well as at a single, readily accessible, temperature with an insensitivity to temperature drift, (3) its potential operation in a heat-sunk configuration allowing operation to a surface temperature of 80°C even in highly elevated temperature environments (in sharp contrast to metal oxide sensors), (4) its ease of coating with diversity of clearly mapped gas-selective materials for form sensor arrays, (5) its low cost of fabrication and operation, (6) its low power consumption, (7) its ease of rejuvenation following contamination, and (8) its ability to rapidly assess false positives using FFT techniques, operating the sensor in a pulsed gas mode.