There are considerable interests to detect and monitor the abnormal level of minerals in water for avoiding/preventing any toxic effects after consumption. Herein, we report the fabrication of solution-gated field-effect-transistor (FET) based potassium sensor using iron oxide nanoparticles (Fe2O3 NPs) modified directly grown zinc oxide nanorods (ZnO NRs). The Fe2O3 NPs modification of ZnO NRs provided stability to nanorods surface and improved surface area for valinomycin immobilization. As-fabricated potassium sensor (valinomycin-Fe2O3 NPs-ZnO NRs/SiO2/Si) provided enhanced current response with increasing potassium concentration. During sensing measurements, FET sensor showed high sensitivity (4.65 mu A/mu M/cm(2)) in the linear range of 0.1 mu M to 125 mu M, low limit of detection (similar to 0.04 mu M), good stability, excellent reproducibility, and favorable selectivity. Thus, good sensing performance of the FET based potassium sensor presents it as simple, low-cost, and convenient device for selective detection of potassium in solution. (C) 2018 Elsevier Inc. All rights reserved.