The NO₂ sensing properties and operational mechanism of the hybrid formed from poly(3-hexylthiophene) (P3HT) and zinc oxide–graphene oxide (ZnO@GO) nanoparticles were investigated. We prepared graphene oxide (GO) and zinc oxide (ZnO) core–shell nanostructured particles with ionic aggregation. Gas sensors were fabricated by spin coating a mixture of P3HT with ZnO@GO on oxide-coated silicon wafers leading to formation of organic field-effect transistors (OFETs). The NO₂ sensing properties of the obtained devices were investigated at room temperature. By means of observing conductance changes before and after exposure to NO₂, it was demonstrated that the hybrid of P3HT with 60 wt% ZnO@GO composites exhibits 210% sensing response to 5 ppm NO₂ gas exposure for 5 min at room temperature. The sensing mechanism included a contribution from the hybrid that was not observed from pure P3HT or by adding either ZnO or GO alone.