By introducing bulky 2-phenylethyl groups into sulfur-rich electron acceptors, 5,5-bithiazolidinylidene-2,2-dione-4,4-dithione and 5,5-bithiazolidinylidene-2,4,2,4-tetrathione, electron transport with the mobility of 0.27 cm(2) V-1 s(-1) with ambient and long-term stability is achieved in thin-film transistors. Bulky groups destroy the intermolecular S-S network, but the long-term transistor stability is maintained. Here, benzyl groups realize one-dimensional stacking structures, whereas 2-phenylethyl groups lead to herringbone structures.