A novel liquid crystal semiconductor (LCS) has been developed under the collaboration with Kanto Chemicals Co. Ltd. The LCS was applied to “top-contact/bottom-gate” type field-effect transistor (FET) to investigate operation and on/off ratio of the FET with Osaka University. The LCS, a long-chain substituted dithienylnaphthalene, shows the fast hole mobility of 0.1 cm² V ^-1s^-1 in the plastic mesophase. Our FET shows the hole mobility of 0.14 cm² V ^-1s^-1 at room temperature, which is in the top class mobility of FETs made of LCS. The LCS characterized both by good solubility into various organic solvents and by "defect-free" property for electronic charge transport. The LCS is expected to become a novel organic semiconductor for high-performance devices.