The conductivity of PEDOT:PSS films was significantly enhanced from 0.3 S cm(-1) to 3065 S cm(-1) through a treatment with dilute sulfuric acids. PEDOT: PSS films with a sheet resistance of 39 O sq(-1) and transparency of around 80% at 550 nm are obtained. These PEDOT: PSS films with conductivity and transparency comparable to ITO can replace ITO as the transparent electrode of optoelectronic devices.