High charge carrier mobility in organic semiconductors is usually accomplished by its high crystallinity, yet, which, often leads to poor mechanical resilience, limiting their performance in flexible devices. In this work, a naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole (NT)-based polymer PNztDTV containing multiple vinyl linkages was reported, exhibiting excellent ambipolar OFET performance, with hole and electron mobility up to 1.0 (μh) and 0.4 (μe) cm2 V–1 s–1, respectively. The GIWAXS analysis revealed overall a rather weak crystallinity in its thin film, yet with considerably strong localized π–π intermolecular interaction. The simultaneous low crystallinity and high performance of PNztDTV imply promising potential in flexible electronics, which is presumably resulted by the isomerization of the vinylene linkage and π-expanded NT core.