GexSi1−xalloy layers grown on (100) silicon substrates by molecular beam epitaxy and amorphized by ion irradiation at −196 °C are shown to recrystallize epitaxially during subsequent ion irradiation at 275 °C. This ion beam annealing process has been examined for two different sample configurations: the first consisting of a thin amorphous layer extending from the surface to about half the thickness of the alloy layer, and the second consisting of a thick amorphous layer extending beyond the alloy layer into the underlying silicon. In both cases, ion beam annealing results in epitaxial crystallization of the alloy layer. Results are reported for alloy composition in the range from Ge0.1Si0.9to Ge0.8Si0.2.