The main idea of this paper is proposing a model to develop generation units considering power system stability enhancement. The proposed model consists of two parts. In the first part, the indexes of generation expansion planning are ensured. Also, small-signal stability indexes are processed in the second part of the model. Stability necessities of power network are supplied by applying a set of robustness and performance criteria of damping. Two parts of the model are formulated as two-objective function optimization that is solved by adaptive non-dominated sorting genetic method-III (ANSGM-III). For better decision-making of the final solution of generation units, a set of Pareto-points have been extracted by ANSGM-III. To select an optimal solution among Pareto-set, an analytical hierarchy style is employed. Two objective functions are compared and suitable weights are allocated. Numerical studies are carried out on two test systems, 68-bus and 118-bus power network. The values of generation expansion planning cost and system stability index have been studied in different cases and three different scenarios. Studies show that, for example, in the 68-bus system for the case of system load growth of 5%, the cost of generation expansion planning for the proposed model increased by 7.7% compared to the previous method due to stability modes consideration and the small-signal stability index has been improved by 6.7%. The proposed model is survived with the presence of a wide-area stabilizer (WAS) for damping of oscillations. The effect of WAS latency on expansion programs is evaluated with different amounts of delay times.