The application of an electric field was found to markedly increase the sensitivity of a gas sensor system. Multi-walled carbon nanotubes (MWCNTs) were used as a gas-sensing material in order to detect a target nitrogen monoxide (NO) gas. The response of the gas sensor was evaluated under both positive and negative electric fields at various applied voltages. The responsiveness of the gas sensor increased by a factor of 2.5 as a function of increasing positive electric fields because of the optimized electron acceptor-donor reaction between the NO gas and the MWCNTs. It was concluded that the applied electric field accelerated the electron transfer between the NO gas and the MWCNTs. (c) 2010 Elsevier B.V. All rights reserved.