The synthesis, characterization, and solid-state morphology of regioregular, amphiphilic polythiophenes based on 3-dodecyl-3'-(3,6,9,12-tetraoxatridecanyl)-2',5-bithiophene are described. These polythiophenes form stable monolayers on the water subphase of a Langmuir trough and are transferable (Langmuir-Blodgett deposition) to solid substrates to give highly ordered thin films. Mixing of the amphiphilic, regioregular polythiophenes with a nonconducting poly(ethylene glycol), in a 50/50 weight percent ratio, results in the formation of a semiconducting network of polythiophene in the Langmuir-Blodgett film. The solution-cast films of the amphiphilic,,regioregular polythiophenes exhibit, liquid-crystalline lamellar mesophases with thermotropic transitions at 0, 60, and 120 degreesC. These transitions are attributed to the melting of the tetraethylene glycol monomethyl ether side chains, the dodecyl side chains, and the polythiophene backbones, respectively. DSC, X-ray diffraction, and optical microscopy were used to identify the thermotropic transitions. The molecular ordering was investigated with X-ray and electron diffraction. Potentially, the regioregular, amphiphilic polythiophenes are applicable as efficient material in field-effect transistors.