The density of misfit dislocation sources in strained Si1−xGexlayers grown on Si substrates is rarely sufficient to explain the observed extent of relaxation when layer thicknesses are in excess of the metastable critical thickness. This letter describes a process whereby a small, but finite number of misfit dislocation nucleation sources can lead to extensive strain relaxation across a complete wafer. Two novel mechanisms for misfit dislocation multiplication are presented and shown to be compatible with microscopic observations of chemically etched layers.