The organic semiconductor 5,5'-Bis(4-hexylphenyl)-2,2'-bithiophene (6PTTP6) shows a remarkable 2D growth mechanism. Without requiring a complicated fabrication process, organic field-effect transistors (OFETs) with only a 1.5 monolayer 6PTTP6 film show mobilities close to those of conventional thick OFETs. Our heterostructured OFET blend exhibits a much faster response speed and a higher sensitivity to nerve-agent simulants than thicker OFET analogues.