Dual-V_th design is an effective leakage power reduction technique at behavioral synthesis level. It allows designers to replace modules on non-critical path with the high-V_th implementation. However, the existing constructive algorithms fail to find the optimal solution due to the complexity of the problem and do not consider the on-chip temperature variation. In this paper, we propose a two-stage thermal-dependent leakage power minimization algorithm by using dual-V_th library during behavioral synthesis. In the first stage, we quantitatively evaluate the timing impact on other modules caused by replacing certain modules with high V_th. Based on this analysis and the characteristics of the dual-V_th module library, we generate a small set of candidate solutions for the module replacement. Then in the second stage, we obtain the on-chip thermal information from thermal-aware floorplanning and thermal analysis to select the final solution from the candidate set. Experimental results show an average of 17.8% saving in leakage power consumption and a slightly shorter runtime compared to the best known work. In most cases, our algorithm can actually find the optimal solutions obtained from a complete solution space exploration.