The monolithic integration of III-V semiconductors on Si emerges as a promising approach for realizing photonic integrated circuits. However, the performance and reliability of epitaxially grown devices on Si are hampered by the threading dislocation density (TDD) generated during the growth. In this study, we evaluated the efficiency of a structure, combining III-Sb-based insertion layers and thermal annealing, on the reduction of the emerging TDD in GaSb buffer layers grown on Si(001) substrates by molecular beam epitaxy. We extensively explored the impact of the thickness, composition and number of the insertion layers. Then a detailed study of the annealing cycles with different conditions was conducted. We ultimately demonstrate a record TDD in the low 1E7 cm-2 for a 2.25 µm GaSb buffer grown on Si(001).