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In this paper, the solid-state urea biosensor was successfully fabricated based on the differential method, which contains three parts: the SnO2/ITO glass electrode used as the pseudoreference electrode; the SnO2/ITO glass electrode used as the contrast electrode; and the urease/SnO2/ITO glass electrode used as the enzyme electrode. Correspondingly, this solid-state urea biosensor was fabricated based on the SnO2/ITO glass electrode, whose simple fabrication process reduces the cost of fabricating the solid-state biosensor. Additionally, as revealed in the experimental results, the solid-state urea biosensor has good sensing characteristics between 5 and 80 mg/dl. After fabricating a successful solid-state urea biosensor, an array sensing system was designed to enhance the precision of the solid-state urea biosensor, which comprises four parts: the biosensor system, the input buffer circuit, the differential circuit, and the weighted sum circuit. As indicated in the experimental results of the array sensing system, the sensing characteristic of the array sensing system is similar to the mean sensing characteristic from four solid-state biosensors. Therefore, the sensing signal of the solid-state urea biosensor can be averaged using the array sensing system. In summary, this study successfully investigated a solid-state urea biosensor and designed an array sensing system to increase the precision of solid-state urea biosensors.