A solid-state electrochemical transistor (ECT) was fabricated using a -conjugated polymer Langmuir-Blodgett (LB) film, which was constructed from poly(N-dodecylacrylamide) (pDDA) and regioregular-poly(3-hexylthiophene) (RR-PHT) mixture. The -conjugated polymer LB film was used as a channel layer and poly(ethylene oxide):LiClO 4 was used as a solid electrolyte. The ECT showed an on/off ratio of 2:3 Â 10 3 and a mobility of 7:7 Â 10 À2 cm 2 V À1 s À1 at a low gate voltage (V G ¼ À2:0 V) with a low charge consumption (1:8 Â 10 À9 mol of e À1 cm À2 ). Moreover, a clear saturation behavior was observed in the ECT. The saturation behavior was derived from the partial dedoping of RR-PHT located at the drain electrode because of the long channel length and low conductivity of the LB film. The low operation voltage with a clear saturation behavior is favorable for applying the ECT to the fabrication of a disposable sensor. #