Abstract
A viscosity sensing system includes a transistor type viscosity sensor, a measurement unit, and a processing unit. The transistor type viscosity sensor includes a semiconductor structure, a source, and a drain. The semiconductor structure includes a GaN layer and an AlGaN layer disposed on the GaN layer and has a gate region between the source and the drain. The gate region of the semiconductor structure has an exposed surface for being contact with a fluid. The measurement unit is electrically connected to the source and the drain and used to measure the electrical signal of the semiconductor structure. The processing unit is coupled to the measurement unit and used to determine the viscosity of the fluid contact with the exposed surface of the gate region according to the electrical signal measured by the measurement unit.