With the advent of three dimensional (3D) IC designs, new partitioning techniques that can take into account the 3D nature of designs are required. In this paper, a new force-directed simulated annealing (FSA) is introduced and used for 3D partitioning. The proposed force-directed simulated annealing introduces force as a new factor during the annealing process and replaces the random moves by probabilistic force-directed moves. Experimental results show that the force-directed move strategy speeds up the convergence and significantly improves the execution time of SA maintaining the quality of solution. FSA algorithm is effective for 3D IC partitioning and can be applied in other optimization problems.