This paper presents experimental results that demonstrate the sensing capability of a multi-walled carbon nanotube (MWCNT). A MEMS-based fabrication process was developed to fabricate a device where a single MWCNT was precisely assembled across a gap. The device could be used either as a chemical-or a flow sensor depending on design and fabrication process. A MWCNT that experienced an electrical breakdown sensitively reacted to gaseous environment. A MWCNT suspended by the dry etching of substrate functioned as a physical sensor to detect N/sub 2/ gas flow. Device fabrication process is suitable to the mass production of CNT-based NEMS/MEMS devices.