We report a simple and inexpensive approach to directly assemble arrays of cadmium sulfide (CdS) semiconductors onto transparent flexible poly(ethylene terephthalate) (PET) sheets via a polymer-mediated selective nucleation and growth process from an aqueous solution. This strategy of assembling functional materials onto plastics utilizes the surface functional molecules of the UV photooxidation patterned polymer to direct the nucleation and growth of CdS. We demonstrated that Such assembled structures are viable for flexible macroelectronics, as manifested by the fabrication of CdS photodetector arrays on PET that can withstand bending. The best devices exhibited a specific detectivity of 3 x 10(11) cm Hz(1/2) W-1 dat 514-nm excitation wavelength at a modulation frequency of 90 Hz at room temperature. This direct assembly strategy eliminates additional lithography and etching steps during the deposition of the active inorganic semiconductor layer, is general to other inorganic materials and plastic substrates, and can enable low-cost, wearable, and/or disposable flexible electronics.