Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most successful conducting polymers due to its appealing properties, such as high conductivity, high transmittance in the visible, good thermal stability, and easy processing from aqueous dispersions. Due to these properties, PEDOT:PSS has shown great potential as an electroactive component for a new generation of biomedical devices. Nonetheless, PEDOT:PSS thin films often suffer from both poor structural resistance in aqueous/biological medium and insufficient electric conductivity for some applications. In this work, we present a new and simple method that can lead to PEDOT:PSS water-resistant films with remarkable enhanced electrical conductivity (increase from 0.2 S/cm to 350 S/cm) and good transparency, consisting of using an oxetane reagent as a cross-linker for PSS. The method brings advantages in comparison with reported ones on conductivity enhancements of PEDOT:PSS using harsh approaches. The improvements on the electric conductivity and stability in aqueous medium are interpreted on the basis of 1H-NMR, Raman spectroscopy, and Atomic Force Microscopy studies.