This paper deals with the tests of carbon nanotube field effect transistors (CNTFETs) for gas sensing applications, exploiting an original sensing technique to dramatically improve selectivity. Such devices exploit the extremely gas-sensitive change of the Schottky barrier heights between carbon nanotubes (CNTs) and drain source metal electrodes. This effect is at the origin of the change of the CNTFET transfer characteristics. Indeed the main effect is related to the gas adsorption creating an interfacial dipole that modifies the Fermi levels alignment and so the bending and the height of the Schottky barrier at the contacts with the CNTs. This change is strictly dependent on the metal/CNTs junction and on the gas involved. We have fabricated on the same chip an array of four CNTFETs composed of four different metals (Pd, Pt, Au, Ti) as electrodes and we have demonstrated that each CNTFET interacts in a very specific way, identifying a sort of electronics fingerprinting. This array has been tested after exposure to NO2, NH3 and di-methyl-methyl-phosphonate (DMMP, a sarin gas simulant) with gas concentrations varying from 10 ppb to 10 ppm using air as gas carrier.