As a family of conjugated polymers, poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) has been extensively investigated because of its high conductivity, solution processability, mechanical flexibility and transparency. However, poor chemical stability makes this conducting polymer difficult for practical application. In addition, a harsh doping condition (eg, aqueous H₂SO₄) is required to obtain high conductivity. By employing perfluorooctane sulfonic acid (PFOSA) as a mild dopant, we were able to fabricate a PEDOT:PSS film with high conductivity (ca. 1700 S/cm) as well as significantly improved chemical and long term stability. The results of detailed spectroscopic and morphological studies show that the superhydrophobic tails and hydrophilic headgroups of PFOSA in the doped PEDOT:PSS are critical factors responsible for the improved properties of the conducting polymer. Finally, owing to its mild nature, PFOSA doping can be employed to fabricate a transparent, flexible and conducting PEDOT:PSS coated PET film.