Benzobisthiadiazole (BBT) is a widely used building block for its high electron affinity and planar configuration. BBT-based copolymers have resulted in good performance of organic field-effect transistors (OFETs). However, devices of these polymers are usually unstable in ambient air since most of these BBT-based polymers have high-lying HOMO energy levels (-4.3 to -4.8 eV). Besides, the field-effect transistors (FET) of BBT-based polymers show relatively low on/off ratios (10(2)-10(4)). As a result, it is very attractive to couple BBT with an electron-deficient block to construct new polymers with air stability. 2,2'-Bithiazole (BTz) is a potential building block due to its electron deficiency and trans-planar configuration. But incorporating 2,2'-bithiazole into polymers still remains a challenge since the organic tin compound of bithiazole is difficult to synthesize. In this article, we successfully prepared 5,5'-bis(trimethylstannyl)-2,2'-bithiazole by a three-step method and then synthesized two benzobisthiadiazole-alt-bithiazole copolymers (P1 and P2). Both P1 and P2 have a low-lying HOMO energy level (-5.3 eV), leading to air stability. Moreover the resulting FETs exhibit a very high on/off ratio (10(5)-10(7)) and a good hole mobility of up to 0.11 cm(2) V-1 s(-1), which represents a significant advancement for BBT-containing polymers.