The formation of self-assembled InAs quantum dots is investigated as the growth time increases from 3.6 to 12 seconds at a low growth rate. The morphological evolution from a rough surface at a short length scale to an extended 2D InAs flat area, and finally to the 3D InAs islands is followed using atomic force microscopy, photoluminescence and transmission electron microscopy. We show that micrometer long terraces with 2 and 3 monolayers thicknesses can co-exist even though 3 monolayers is beyond the critical thickness. As the quantum dots are nucleated the 3 monolayers thick terrace is depleted by the 3D islands.