The reduction of threading dislocation density due to their mutual interactions in GaSb thin films grown on (001) GaAs substrates by molecular beam epitaxy has been investigated. The effectiveness of several buffer layer schemes including GaSb/AlSb strained layer superlattice and In0.11Ga0.89Sb/GaAs buffers for threading dislocation suppression was evaluated. High-resolution transmission electron microscopy shows that the GaSb/GaAs interface consists of a highly periodic network of 90 degrees pure edge misfit dislocations, with an average spacing close to that or a fully relaxed system. This results in relatively low threading densities in the GaSb epilayer, despite their large lattice constant mismatch (8.2%). The threading dislocation density as a function of GaSb film thickness was determined by plan-view transmission electron microscopy and was found to decrease with film thickness due to mutual interactions among dislocations. It was found that a strained layer superlattice of GaSb/AlSb, with each layer close to its critical thickness, is the most effective in threading density reduction.