Charge–Transfer (CT) complexes are stabilized by partial transfer of electric charges from donor molecules to acceptor molecules. The conductivity of the film of CT-complexes can be controlled if the degree of charge transfer is varied by applying an external field, for example an electric field. In this study, we fabricated field-effect transistors (FETs) using CT complex Langmuir–Blodgett (LB) films (TMPD-CnTCNQ), and have attempted to control the conductivity of the CT-complex layers by gate voltages. The temperature dependence of conductivity shows that semiconducting and metallic parts coexist in parallel between the electrodes.