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By coating one side of the surface of a ZnO nanobelt ͑NB͒ with multilayer polymers using an electrostatic self-assembling process, a humidity/chemical nanosensor based on piezoelectric field effect transistor ͑PE-FET͒ is demonstrated. The working principle of the PE-FET relies on the self-contraction/expansion of the polymer, which builds up a strain in the piezoelectric NB and induces a potential drop across the NB that serves as the gate voltage for controlling the current flowing through the NB. The response of PE-FET to the phase transition of the coating polymer was also demonstrated. The device is a component for nanopiezotronics.Devices using one dimensional nanostructure, such as nanowire ͑NW͒ and nanobelt ͑NB͒ ͑Ref. 1͒ are being extensively studied due to their supreme performance different devices. Prototype devices have been demonstrated using NWs and NBs as FET, 2 thermal transistor, 3 field emission device, 4 and biological sensors. 5 Among the materials that are extensively studied in nanoscience, ZnO is perhaps one of the most important materials, and it has been applied for fabricating different electronic transistors 6 and chemical sensors. 7 Most recently, a research direction termed of nanopiezotronics has been coined based on the piezoelectric-semiconducting coupled properties of ZnO NWs and NBs for fabricating unique electronic components. 8 The first application of nanopiezotronics is the piezoelectric nanogenerator based on ZnO NWs, 9 which demonstrates a unique approach of converting nanoscale mechanical energy into electric energy and harvesting energy from the environment for self-powered nanosystems. 10 PE-FET and diodes 12 that operate based on the coupling effect of piezoelectric and semiconducting properties of ZnO have been developed.In this letter, we demonstrate a humidity/chemical sensor based on PE-FET. 11 The devices were based on a single-side coated ZnO NB functionalized with multilayers of polymers. Upon exposure to high humidity vapors, the polymers swell and produce an asymmetric strain across the ZnO NB. In return, the deformation of ZnO NB produces a piezoelectric field across the NB, which serves as the gate for controlling the flow of current along the NB. This is the working principle of the polymer functionalized PE-FET.Polymers for functionalization of NB are anionically charged polyN-isopropylacrylamide ͑PNIPAM͒ and poly͑diallyldimethylammonium chloride͒ ͑PDADMAC͒. PNIPAM is the most well known temperature sensitive polymer in aqueous solution, which exhibits a lower critical solution temperature ͑LCST͒ of around 32°C. 13 The volume change ratio of a cross-linked PNIPAM corresponding to its hydra-tion and dehydration transition can reach as high as 20 times. 14,15 In order to introduce charge groups in the polymer chain, acrylic acid sodium salt was copolymerized with NIPAM monomer at a molar ratio of 1:9.In the experiments, our devices were fabricated with described previous method. 16 During the layer-by-layer assembly experiment, ZnO was first immersed in a dilu...