Recently synthesized benzo-annulated fused oligothiophenes and oligoselenophenes are introduced as air-stable organic semiconductors for high-performance organic field-effect transistors. To evaluate electronic mobility intrinsic to the materials, single-crystal transistors are prepared for two representative compounds of benzo-annulated pentathienoacene f-B5TB and its selenium analogue f-BT3STB. High mobility of more than 1 cm2/Vs is achieved for the selenium compound, due to its considerable Se- - -Se orbital interactions. The transistor performances have been stable for two months, indicating high duration of the compound in the ambient atmosphere. Copyright © 2007 Materials Research Society.