InAs layers, grown on GaAs substrates using molecular beam epitaxy, has been systematically investigated. Through the observation of pyrometer readings, it was found that the transition of both the growth mode and the surface morphology of InAs layers are strongly dependent on the As-4/In flux ratio and the substrate temperature. Cross-sectional transmission electron microscopy images showed that effective reduction in defect density resulting from the InAs/GaAs interface was achieved for InAs layers with a thickness of only 1.5 mum.