This paper deals with the effect of negative gate bias stress with different times on the Carbon Nanotube FieldEffect Transistor (CNTFET) based gas sensors, obtained using Single-Walled Carbon Nanotubes (SWCNTs) matsas channel. The effects of Gate Bias Stress (GBS) on transistor performance are important; hence it is necessary tounderstand how our device behaves under bias stress. To perform this work, I-V characteristics, are taken byapplying a constant gate voltage (Vgs) for an extended time. I-V characteristics after stress exhibited an identicalshape to the one before stress with an important degradation of the current that flows through the transistors. Apossible source of the Bias Stress Effect (BSE) is traps in the semiconductor itself which are spatially and energeticallyisolated due to the disorder of SWCNTs. This hypothesis will be confirmed by the saturation of thedrain current shift ΔI after a prolonged period of time. All isolated trap states are saturated and only electricaltraps still active and give us the original I-V characteristics.