In order to continue the performance enhancement of Si-based semiconductor devices, the number of devices on a chip as well as the performance of those devices must continue to improve. One method for improving device functionality is the incorporation of strained Si-Ge heterostructures. While such heterostructures have been the focus of much research in planar Si processing, only recently has the fabrication of such heterostructures in nanoscale semiconductors been addressed. In particular, the fabrication of a Si-Ge radial nanowire heterostructure requires a consideration of the epitaxial stability of the shell on the underlying core nanowire. This work develops a model for the strain state of a radial nanowire heterostructure, focusing on the particular example of Si-Ge. The behavior of the radial nanowire heterostructure is compared to that of a planar heterostructure, and we find that much higher strains can be achieved in the nanowire geometry. (c) 2008 Elsevier B.V. All rights reserved.