The authors present a patterning technique for isolating organic field-effect transistors via an ultraviolet/ozone process. The technique relies on the conversion of a poly(dimethylsiloxane) (PDMS) film to a silicon oxide (SiOx) which provides the selective growth of pentacene thin films on hydrophobic and smooth PDMS and hydrophilic and rough SiOx created by photoinduced conversion of the PDMS. They demonstrate that pentacene films grown on PDMS have five times greater channel conductivity than those grown on the SiOx film, and this difference in performance can be exploited to partially pattern active devices and reduce leakage using a photopatterning technique.