Tetracyanoquinodimethane (TCNQ) complexes of fluorene, dibenzofuran, dibenzothiophene, terphenyl, dithienothiophene, and carbazole show n-channel transistor properties, whereas that of diaminoterphenyl and phenothiazine exhibits ambipolar characteristics. Ambipolar transport is observed when the highest occupied molecular orbital (HOMO) level of the donor–acceptor complex is located above the ordinary hole transport limit. Since the HOMO of the charge-transfer complex is deeper than that of the component donor owing to the charge-transfer interaction, not all hole-transporting materials show hole transport in the charge-transfer complexes. In addition, the effective (super-exchange) transfer integrals have to be sufficiently large; this is frequently not satisfied when the donor HOMO is practically orthogonal to the acceptor’s lowest unoccupied molecular orbital (LUMO). By applying these criteria to calculations starting from the crystal structures, transistor properties of mixed stack charge-transfer complexes are explained.