This paper presents the experimental and numerical study of the behavior of a semi-connected steel shear wall in a self-centering steel frame, a new lateral load-resisting system. In this setting the shear wall is connected only to the floor beam. Steel shear walls exhibit high ductility and energy dissipation capacity, but suffer from large residual displacements. To solve this problem, the proposed system places the shear wall inside a post-tensioned steel frame, which makes the structure self-centering and has little residual drift. The main mechanical parameters, including yield strength, ultimate strength, residual displacement, effective stiffness, equivalent viscous damping ratio and energy dissipation were determined by cyclic loading tests of a one-span one-story specimen. The performance of the proposed system is also compared with a conventional steel shear wall. The results show that the self-centering capacity of the new system is 2-3 times larger than that of a conventional wall. Moreover, the dissipated energy of the proposed system was approximately 1.5 times that of the simple one.The damping ratio of the system was about 0.17, almost the same as the conventional system at ultimate loading cycles. Furthermore, the system behavior was successfully predicted by a numerical model developed in Abaqus with errors of less than 14%.