A novel type of electrochemical sensor for detection of phosphate in water environment was developed by combining the interfacial barrier of p-n junction with the adsorption of phosphate. The electrochemical response was produced by the induced change of the barrier height, which was only caused by the specific adsorption of phosphate. Two linear concentration ranges (0-0.045 mg L-1 and 0.045-0.090 mg L-1) with two sensitivities (4.98 μA (μg L-1)-1 and 1.28 μA (μg L-1)-1) were found. The good performance made the sensor meet the requirements of the World Health Organization for drinking water (1 mg L-1 of phosphate). It is an approach to develop electrochemical sensors by employing the interfacial barrier effects on electrochemistry.