Dynamic characteristics are extremely important for design and operation of thermoelectric coolers (TECs). This paper develops a three-dimensional transient TEC model based on the coupling of heat transfer and electric conduction within semiconductors. The model takes into account all thermoelectric effects, including Joule heating, Thomson effect, Peltier effect and Fourier's heat conduction. For most of semiconductor materials, Seebeck coefficient, electric conductivity and thermal conductivity are strongly temperature-dependent. Therefore, the present transient model is used to compare dynamic temperature variations at the cold and hot ends with constant and variable material properties. Small, medium, and large applied currents with various cooling loads are adopted as operating conditions. The results show that, at small currents, constant property model developed by this work can predict accurately the dynamic characteristics, however, with the increase in current, the temperature-dependence of properties have more and more remarkable effect on the dynamic temperature variations, especially for high cooling loads. When the current is larger than a specific value, the heat transferred from the hot end to the cold end by Fourier's heat conduction will exceed the heat adsorbed at the cold end by Peltier effect, thus, the temperatures at the cold and hot ends increase continuously, the TEC cannot reach the steady-state. This phenomena is predicted exactly by the variable property model, oppositely, the constant property model predicts that the TEC still supply refrigeration. (c) 2013 Elsevier Ltd. All rights reserved.