Antiphase boundaries free GaSb epitaxial layers with low surface roughness (< 0.5 nm) have been synthesized on standard microelectronic 300 mm nominal (001)-Si substrates by metal organic chemical vapor deposition using a two-step growth process. By adjusting the growth temperature and the thickness of the nucleation layer, antiphase boundary free GaSb layers as thin as 250 nm are obtained. The 12% lattice mismatch between GaSb and Si is accommodated by both the formation of threading dislocations and a periodic array of 90 degrees misfit dislocations at the interface. A GaSb layer inserted between AlSb barriers has been grown on an optimized GaSb/(001)-Si buffer layer and exhibits room temperature photoluminescence.