Ultrathin, conformal semiconductor-dielectric bilayers can be fabricated in one step by self-organization (see Figure), without exposing the critical interface to ambient contamination. Low-voltage polymer field-effect transistors using a fluorene-triarylamine copolymer as the p-channel semiconductor and 40-60 nm thick crosslinked bisbenzocyclobutene derivative as the gate dielectric are shown to be robust and reproducible.