This study is the first to report on the detection of biogenic amines in an aqueous solution using an organic field-effect transistor (OFET) device with an extended gate electrode modified with a layer of diamine oxidase and a horseradish peroxidase osmium-redox polymer. The limit of detection (LOD) for histamine was estimated to be 1.2 μM. These results reveal that extended-gate type OFET devices are highly suitable enzyme-based biosensors for the detection of biogenic amine levels.