Features of the I-V characteristics and the electrical properties of electronics-grade carbon nanotube (EG-CNT) sensors, which were fabricated and integrated in micro fluidic system by combining MEMS-compatible fabrication technology with AC dielectrophoresis technique, were investigated at room temperature to account for significant Joule heating effect under high activation current. The experimental results together with the traditional heat transfer theory indicate that the nonlinearity of the I-V curves and the negative resistance change of the EG-CNT sensors are basically induced and controlled by the thermal effect. In particular, it was found that the lower the original resistance of EG-CNT sensors, the higher the normalized resistance change and lower the sensor's time response. Then, the sensor's capability for aqueous flow detection was exploited upon exposure to DI-water flow in micro fluidic system. The operation power of the sensors was found to be extremely low, i.e., in the range of mu W. Furthermore, higher activation power may degrade the sensor's responsivity.