We present the fabrication and characterization of a membrane-type surface stress sensor (MSS), arranged in arrays for molecular detection in gaseous phase. Made out of SOI substrate, a round membrane with a diameter of 500 mu m and a thickness of 2.5 mu m is suspended by four sensing beams with integrated p-type piezoresistors, composing a full Wheatstone bridge. The membrane is coated with a thin polymer layer, which reacts with volatile molecules and produces a deflection of the membrane. Accumulated mechanical stress due to the deflection is applied on the sensing beams. MSS were functionalized with cellulose acetate butyrate (CAB) by inkjet spotting. They were characterized in a humidity chamber and showed a fast response time of 1.3 s for a relative humidity transition from 0% to 62%. Moreover, the membrane response is linear with a sensitivity of 87 mV/%RH. (C) 2012 Elsevier Ltd....Selection and/or peer-review under responsibility of the Symposium Cracoviense Sp. z.o.o.