A new n-channel semiconductor class for organic field-effect transistors (OFETs) based on thienoquinoidal structures is reported. A newly employed terminal group, the ((alkyloxy)carbonyl)cyanomethylene moiety, plays two important roles in the thienoquinoidal compounds: i.e., as an electron-withdrawing group to keep the LUMO energy level sufficiently low for acting as an n-channel organic semiconductor and as a solubilizing group to facilitate solution processability. For the construction of this class of compounds, a new, straightforward synthetic method was established and applied to oligothienoquinoidal and fused thienoquinoidal systems. When both core and alkyl groups in the ester moiety were tuned, the thienoquinoidals exhibited good solubility, stability in the atmosphere, and electron-accepting properties, as well as solution processability. Solution-processed FETs based on the terthienoquinoid derivative with ((n-alkyloxy)carbonyl)cyanomethylene moieties exhibit good electron mobilities (mu similar to 0.015 cm(2) V-1 s(-1)) and I-on/I-off approximate to 10(5) under ambient conditions. Vapor-processed FETs using the benzodithienoquinoidal derivative showed similar n-channel FET characteristics.