This contribution deals with Carbon Nanotubes Field Effect transistors (CNTFETs) based gas sensors fabricated using a completely new dynamic spray based technique (patented) for SWCNTs deposition. The extreme novelty is that our technique is compatible with large surfaces, flexible substrates and allows to fabricate high performances transistors exploiting the percolation effect of the SWCNTs networks achieved with extremely reproducible characteristics. Recently, we have been able to achieve extremely selective measurement of NO2, NH3 and CO using four CNTFETS fabricated using different metals as electrodes, exploiting the specific interaction between gas and metal/SWCNT junctions. In this way we have identify an electronic fingerprinting of the gas detected. The response time is evaluated at less than 30sec.