A viscosity measurement system, which is for measuring the viscosity of a fluid, comprises a transistor-type viscosity sensor, an electrical measurement unit, and a processing unit. The transistor-type viscosity sensor includes a semiconductor structure, a source terminal, and a drain terminal. The semiconductor structure includes a GaN layer and an AlGaN layer disposed on the GaN layer. The portion of the semiconductor structure that is between the source terminal and the drain terminal has a gate region, which has an exposed surface for being in contact with the fluid. The electrical measurement unit is in electrical connection with the source terminal and the drain terminal and for measuring an electronic signal of the semiconductor structure. The processing unit is coupled to the electrical measurement unit and for determining the viscosity of the fluid according to the electronic signal measured.