The strain induced by thermal oxidation in a cylindrical silicon (Si) structure has been studied by high resolution synchrotron x-ray diffraction. The strain in the structure studied is expected to display some of the features that exist in three-dimensional non-planar surfaces in electronic devices. The sample consisted of a 2-dimensional array, with period of 300nm, of approximately cylindrical pillars covered with a thin thermal oxide (thickness ∼6nm). These showed a tensile strain of 3.7×10-4 at room temperature. This strain can be relaxed elastically by chemical removal of the oxide. Process simulation indicates the importance of both the contribution due to interface stress during the oxide growth and stress due to differential thermal contraction during the cooldown. Significant differences exist between the strain in such cylindrical pillars and in a flat wafer.