A novel single-crystal organic field-effect transistor (OFET) is described, in which the gate dielectric is replaced by a thin gap that can be occupied by a gas or vacuum. When used in combination with high-quality rubrene or tetracyanoquinodimethane (TCNQ) crystals, n-and p-devices with extremely good mobilities and normalized sub-threshold slopes, representing the ultimate in OFET performance, are realized.