An organic field-effect transistor (OFET) toward phosphate sensing has been successfully developed. The fabricated OFET possessing an extended-gate functionalized with zinc(II)-dipicolylamine (Zn-II-DPA) exhibited an electrical and cross reactive response to phosphate anions such as nucleotides and inorganic phosphates over halide ions in water. The results obtained here indicate that OFET could be a powerful platform for phosphate sensing based on supramolecular interactions.