Carbon nanotubes(CNT) has chemical stability and great sensitivity characteristics. In particular, the gassensor required characteristics such as rapid, selectivity and sensitivity sensor. Therefore, CNT are ideal materialsto gas sensor. So, we fabricated the NOx gas sensors of MOS-FET type using the MWCNT (multi-walled carbonnanotube). The fabricated sensor was used to detect the NOx gas for the variation of Vgs (gate-source voltage)and electrode changed electrode spacing=30, 60, 90[㎛]. The gas sensor absorbed with the NOx gas moleculesshowed the decrease of resistance, and the sensitivity of sensor was increased by magnification of electrodespacing. Furthermore, when the voltage(Vgs) was applied to the gas sensor, the decrease in resistance wasincreased. On the other hand, the sensor sensitivity for the injection of NOx gas was the highest value at theelectrode spacing 90[㎛]. We also obtained the adsorption energy(Vgs) using the Arrhenius plots by the reduction ofresistance due to the voltage variations. As a result, we obtained that the adsorption energy was increased withthe increment of the applied voltages.