We report here the fabrication of a sensitive and selective gas sensor using a carbon nanotube (CNT) membrane as the gas sensing transducer. A TiN/Al2O3/TiN stack is used as a support for the CNT growth catalyst, evaporated with a 45° tilt angle on the vertical wall. Thanks to this layout, dense and thin arrays of aligned and horizontal CNTs are grown, both selectively and on-site, in between interdigited electrodes. These features allow better gas limit detection with working conditions close to room temperature and atmospheric pressure. The FET or switch like structure of the sensor allows multiple readouts (conductance, capacitance, resonance) to achieve a better selectivity for gas detection.