A promising field-effect transistor (FET) biosensor has been fabricated based on pyruvate oxidase (PyO) functionalized ZnO nanorods (ZnO NRs) array grown on seeded SiO2/Si substrate. The direct and vertically grown ZnO NRs on the seeded SiO2/Si substrate offers high surface area for enhanced PyO immobilization, which further helps to detect phosphate with higher specificity. Under optimum conditions, the fabricated FET biosensor provided a convenient method for phosphate detection with high sensitivity (80.57 mu A mM(-1) cm(-2)) in a wide-linear range (0.1 mu M-7.0 mM). Additionally, it also showed very low effect of electroactive species, stability and good reproducibility. Encouraging results suggest that this approach presents a promising method to be used for field measurements to detect phosphate. (C) 2017 Published by Elsevier Inc.