The gate-voltage-dependence of the drain currentvoltage characteristics have been measured for organic eld-eect transistors(OFETs) based on thick and thin LangmuirBlodgett (LB) lms of octadecyl tetracyano quino dimethane. The obtained results haveindicated that the eld-eect doping phenomena in OFETs with thick and thin LB lms are basically the same with each other. Atheoretical approach based on a simple four-layer model has also be taken to obtain basic understanding of the eld-eect dopingphenomenon in OFETs. Through this approach, it has been suggested that when the organic semiconductor layer is extremely thin,the total amount of the doped charge,Q, deviates from the prediction of the well-known threshold relationship,Q / (VG . Vth),whereVG and Vthare the gate voltage and its threshold value, respectively, but the charges are still localized in the interface regionlike in the case of OFETs with thick semiconductor layers.