It is described an integrated gas sensor device comprising a silicon substrate and an oxide layer on the silicon substrate, as well as a working electrode, a counter electrode and a reference electrode, on the oxide layer, the working electrode and the counter electrode having respective active area exposed to an environmental air through at least a plurality of first openings and a plurality of second openings in the oxide layer in correspondence of the working electrode and of the counter electrode, further comprising an electrolyte layer portion and a hydrogel layer portion on the electrolyte layer portion, the electrolyte and hydrogel layer portions having a same size, suitable to cover at least the working, counter and reference electrodes, the hydrogel layer portion acting as a “quasi solid state” water reservoir.