In this work, we report the selective area epitaxial growth of high quality InP in shallow trench isolation (STI) structures on Si (0 0 1) substrates 6° miscut toward (1 1 1) using a thin Ge buffer layer. We studied the impact of growth rates and steric hindrance effects on the nano-twin formation at the STI side walls. It was found that a too high growth rate induces more nano-twins in the layer and results in InP crystal distortion. The STI side wall tapering angle and the substrate miscut angle induced streric hindrance between the InP facets and the STI side walls also contribute to defect formation. In the [-1 1 0] orientated trenches, when the STI side wall tapering angle is larger than 10°, crystal distortion was observed while the substrate miscut angle has no significant impact on the InP defect formation. In the [-1 1 0] trenches, both the increased STI tapering angle and the substrate miscut angle induce high density of defects. With a small STI tapering angle and a thin Ge layer, we obtained extended defect free InP in the top region of the [1 1 0] trenches with aspect ratio larger than 2.