The invention provides a semiconductor structure, a self-supporting gallium nitride layer, and a preparation method for the semiconductor structure. The method comprises the steps: 1), providing a substrate; 2), forming a multi-quantum-well structure decomposition layer on the upper surface of the substrate, wherein the multi-quantum-well structure decomposition layer at least comprises gallium elements; 3), forming a patterned mask layer on the upper surface of the multi-quantum-well structure decomposition layer; 4), carrying out the processing of the structure obtained at step 3), and enabling the multi-quantum-well structure decomposition layer to be decomposed and reconstructed, so as to obtain a decomposition reconstruction lamination layer. According to the invention, when the semiconductor structure manufactured through the method is used for the growing of gallium nitride, a gallium nitride crystal seed layer in the decomposition reconstruction lamination layer can provide crystal seeds for the subsequent growing of gallium nitride. Holes in the decomposition reconstruction lamination layer facilitate the self-peeling of gallium nitride growing subsequently, and also can reduce the stress between gallium nitride crystal lattices growing subsequently, and can improve the growing quality of gallium nitride.