The electrical conductivity of poly (3,4-ethylenedioxythiophene) doped with poly (4-styrenesulfonate) (PEDOT/PSS) was significantly improved by two orders of magnitude upon addition of ethylene glycol (EG). It was found that the EG was crucially important for (i) crystallization of PEDOT molecules, (ii) removal of the insulating PSS from the surface of the PEDOT/PSS particles, which improved both intra- and inter-particle transfer of charge carriers. Furthermore, Schottky diode, field-effect transistor, microfiber, and soft actuator were fabricated utilizing the highly conductive PEDOT/PSS by means of line patterning, wet-spinning, and cast techniques, respectively.