The cycle models of a single-stage and a two-stage semiconductor thermoelectric refrigeration system are established, based on non-equilibrium thermodynamics. They are used to derive the general expressions of three important performance parameters, such as the coefficient of performance (COP), the rate of refrigeration, and the power input. By using these expressions, the performance of the two-stage thermoelectric refrigeration system is discussed in detail. The maximum COP and rate of refrigeration are calculated, the internal structure parameter of the thermoelectric device is optimized, and the reasonable ranges of some parameters are determined. The results obtained here are compared with those of a single-stage thermoelectric refrigeration system, and consequently the advantages of two-stage thermoelectric refrigerators are expounded.