A method for the growth of high quality GaSb epilayer on GaAs (001) substrate is demonstrated in this study. It is found that a superior GaSb/GaAs interface can be obtained by depositing a thin Sb-precursor layer on the GaAs substrate containing a GaAs buffer layer. It is suggested that the growth occurs via the interface misfit (IMF) growth mode. Without this treatment, GaSb epilayer may grow according to the Stranski-Krastanov mechanism or via a blend of the Stranski-Krastanov and IMF mechanisms, leading to an inferior GaSb/GaAs interface. This could be due to the intermixing of anions, leading to the turbulent composition and misfit dislocation distribution at the heterointerface. It appears that with the addition of a Sb layer, IMF arrays can be formed at GaSb/GaAs interface resulting in superior GaSb layer without the need for changing the growth parameters.