Relaxed InyGa1-yAs epilayers grown on (00 1) GaAs are known to exhibit a cross-hatched surface with ridges running along the [I 10] and [110] directions. We find that Ga1-xMnxAs epilayers grown on such buffer layers can have as-grown Curie temperatures (T-C) that are higher than the as-grown 110 K value typical of Ga1-xMnxAs/GaAs heterostructures. Further, low-temperature annealing leads to only modest additional increases in T-C, contrasting with the behavior in Ga(1-)xMn(x)As/GaAs where T-C typically increases significantly upon annealing. Our observations suggest that the initial concentration of Mn interstitials in as-grown Ga1-xMnxAs/InyGa1-yAs heterostructures is smaller than that in as-grown Ga1-xMnxAs/GaAs heterostructures. We propose that strain-dependent diffusion may drive Mn interstitials from the bulk of the growing crystal to more benign locations on the ridged surface, providing a possible route towards defect-engineering in these materials. (C) 2004 Elsevier B.V. All rights reserved.