A novel easily made thienoacene-based organic semiconductor, i.e., dinaphtho[3,4-d:3′,4′-d′]benzo[1,2-b:4,5-b′]dithiophene (Ph5T2), was synthesized in high yield, and its thermal stability, electrochemical properties, thin-film morphology and field-effect mobility were investigated. Ph5T2 exhibit excellent thermal stability with a decomposition temperature (Td) of 427 °C. Thin-film X-ray diffraction (XRD) and atomic force microscopy (AFM) characterizations indicate that Ph5T2 can form highly ordered films with large domain size on the para-sexiphenyl (6P)-modified substrates. Organic thin-film transistors (OTFTs) with top-contact geometry based on Ph5T2 exhibit mobilities up to 1.2 cm2 V−1 s−1 in ambient. The devices are highly stable and exhibit almost no performance degradation during 3 months storage under ambient conditions with relative humidity up to 80%.Graphical abstractHighlights► High mobility: Ph5T2 is the first fused aromatic comprising seven fused rings which shows mobility beyond 1 cm2 V−1 s−1. ► Great device stability even in ambient with humidity up to 80%. ► Ease of mass preparation and unique chemical structure design.