AbstractWe demonstrate a facile fabrication method to make chemical gas sensors using single‐walled carbon nanotubes (SWNT) electrochemically functionalized with polyaniline (PANI). The potential advantage of this method is to enable targeted functionalization with different materials to allow for creation of high‐density individually addressable nanosensor arrays. PANI‐SWNT network based sensors were tested for on‐line monitoring of ammonia gas. The results show a superior sensitivity of 2.44% ΔR/R per ppmv NH3 (which is more than 60 times higher than intrinsic SWNT based sensors), a detection limit as low as 50 ppbv, and good reproducibility upon repeated exposure to 10 ppmv NH3. The typical response time of the sensors at room temperature is on the order of minutes and the recovery time is a few hours. Higher sensitivities were observed at lower temperatures. These results indicate that electrochemical functionalization of SWNTs provides a promising new method of creating highly advanced nanosensors with improved sensitivity, detection limit, and reproducibility.