Defect-free GaP growth on exact (0 0 1) Si substrates is an important prerequisite for integrating III/V-based optics with Si-based electronics. In the present paper, dynamic electron diffraction in transmission electron microscopy using specific excitation conditions are exploited to unambiguously identify anti-phase domains (APDs) and anti-phase boundaries (APBs) in GaP. These defects are amongst the most critical and detrimental defects when heteroepitaxially growing III/Vs on Si. The geometry of the APDs is correlated to the Si-wafer morphology prior to the Gal? growth as well as to the Gal? nucleation and growth conditions. It is also demonstrated that APDs intersecting the GaP surface can be seen in the scanning probe surface images of these layers as deep trenches, if a suitable annealing procedure is applied. The GaP growth temperature needs to be high enough to allow for the kinking of the APBs away from the {I I 0} planes. Furthermore, the Si surface area covered by monolayer high islands should be as small as possible to initiate self-annihilation of the APBs. Combining optimized GaP growth with optimized Si surface pretreatment, one can realize APD-free GaP on Si after only 40 nm film growth. (C) 2007 Elsevier B.V. All rights reserved.