•Polyurethane containing terphenyl groups affording high-mobility organic thin-film transistor.•Polyurethane containing terphenyl groups can be easily fabricated by solution-processing and cured by UV.•Polyurethane containing terphenyl groups can induce crystallization of sexiphenyl.Novel polyurethane containing terphenyl groups were designed and synthesized as gate insulators to induce the crystallization of p-sexiphenyl(p-6P) for organic thin-film transistors (OTFTs). Different sizes and shapes of p-6P grains were measured by atomic force microscopy (AFM), and results showed that the large size of p-6P grain can improve the performance of OTFTs. About 900 nm thick films can be easily fabricated by spin-coating under ambient conditions, followed by curing at UV irradiation for 10 min. OTFTs with this film as gate insulator were found to have good processability, a high charge-carrier mobility of 1.1 cm2/V s, a threshold voltage of −25 V, and an on/off current ratio >105. The result indicated that this material is a promising candidate for the exploration of devices using OTFTs.Graphical abstractNovel polyurethane containing terphenyl groups were designed and synthesized as gate insulators to induce the crystallization of p-sexiphenyl(p-6P) for organic thin-film transistors (OTFTs). Different sizes and shapes of p-6P grains were measured by atomic force microscopy, and results showed that the large size of p-6P grain can improve the performance of OTFTs. About 900 nm thick films can be easily fabricated by spin-coating under ambient conditions, followed by curing at UV irradiation for 10 min. OTFTs with this film as gate insulator were found to have good processability, a high charge-carrier mobility of 1.1 cm2/V s, a threshold voltage of −25 V, and an on/off current ratio >105. The result indicated that this material is a promising candidate for the exploration of devices using OTFTs.