We report on high performance and stable novel p-type active oligomers for organic thin film transistors based on a structural combination of fused bithiophene with fluorene or biphenyl unit. A higher field-effect mobility and device stability after UV irradiation was achieved with biphenyl end-capped fused bithiophene (BPTT) than the fluorene end-capped derivative (BFTT). Moreever, it is noteworthy that both molecules, especially BPTT, showed a high performance, almost the same or a slight decrease in field effect mobility and I_ON/I_OFF, even after they were kept under ambient conditions for more than one month.