In this article, the NO₂sensing performance of the mixed-potential-type yttria stabilized zirconia (YSZ)-based sensor was improved by modifying the three-phase boundary (TPB). The double-tape casting and the pore-forming method were simultaneously used to obtain the porous YSZ-substrate. Furthermore, a group of tape-casting slurries with different starch concentrations (0 wt%, 5 wt%, 10 wt% and 15 wt%) were applied to form the different contact areas of the three-phase boundary (TPB). The scanning electron microscope (SEM) images showed that YSZ-substrate prepared by using the slurry with 15 wt% starch had the largest contact area. The sensor based on the YSZ-substrate with the largest contact areas and the MnCr₂O₄sensing electrode (SE) showed the largest response compared with the other sensors when they were exposed to 10-500 ppm NO₂at 800 degrees C. The measured polarization (I-V) curves indicated that the present sensors operated under the mixed-potential mechanism. In addition, the sensor showed a good selectivity and repeatability to NO₂.