Stretchable crystalline semiconductors are the key to enable wearable high power and energy devices. The work presented in this thesis evaluates the non-uniform surface stress distribution of stretchable Si and GaN serpentine geometries and has yielded the following contributions: (i.) 2D and 3D numerical analyses of the effect of mechanical anisotropy in (100) Si on crystalline stretchable behavior, revealing the direction can be up to 36% more stretchable than the direction, and (0001) GaN has no anisotropic dependence. (ii.) A micro-fabrication procedure which allows for the fabrication and release of stretchable Si into serpentine mechanical test structures which demonstrated an experimental strain-to-rupture of 84%. (iii.) In-situ stress characterization of the non-uniform surface stress distribution in stretchable Si, while applying external strain, using micro-Raman spectroscopy. (iv.) A micro-scale imaging technique to spectrally and spatially resolve the local surface stress distribution in stretchable AlGaN/ GaN high electron mobility transistors.