In this paper,bottom contact organic thin-film transistor(OTFT)gas sensors were prepared.Silicon dioxide(SiO2)and titanium/aurum(Ti/Au)were used as the insulating layer and the electrode for the device,respectively.The multi-walled carbon nanotubes(MWCNTs)/α-sexithiophene(α-6T)bilayer films were used as the active layer,andα-6T single layer sensitive film was also prepared for comparison purpose.The electrical and trace NO2-sening properties of these two OTFT gas sensors were tested and analyzed.The results showed that,the OTFT device based on MWCNTs/α-6T bilayer had obviously better electrical properties,better stabilities and higher NO2-sening response values than the device withα-6T single layer,in which both the carrier mobility(μ)and on/off current ratio enhanced two order of magnitude.The improved performance of bilayer OTFT can be explained that MWCNTs acted as highly conducting bridges connecting the crystalline terraces in theα-6T film.Threshold voltage(VT),carrier mobility,on/off current ratio and grid current which showed extremely similar variation trend as source-drain current,were optional parameters to reveal the gas-sensing characteristic of OTFT gas sensors.Morphology analysis showed that the special feature of MWCNTs had certain influence on the gas-sensing properties. In this paper, bottom contact organic thin-film transistor (OTFT) gas sensors were prepared. Silicon dioxide (SiO2) and titanium / aurum (Ti / Au) were used as the insulating layer and the electrode for the device, respectively. -walled carbon nanotubes (MWCNTs) / α-sexithiophene (α-6T) bilayer films were used as the active layer, and α-6T single layer sensitive film was also prepared for comparison purpose. Electrical and trace NO2-sening properties of these two OTFT gas sensors were tested and analyzed. The results showed that, the OTFT device based on MWCNTs / α-6T bilayer had obviously better electrical properties, better stabilities and higher NO2-sening response values ​​than the device with α-6T single layer, in which both the carrier mobility (μ) and on / off current ratio enhanced two order of magnitude. The improved performance of bilayer OTFT can be explained that MWCNTs acted as highly conducting bridges connecting the crystalline terraces in the α-6T film.Threshold voltage (VT) , carrier mobi lity, on / off current ratio and grid current which showed extremely similar variation trend as source-drain current, were also able to reveal the gas-sensing characteristic of OTFT gas sensors. Morphology analysis showed that the special feature of MWCNTs had certain influence on the gas-sensing properties.