A double‐crystal x‐ray topograph was used to determine local strain in metal‐oxide‐semiconductor (MOS) transistor test chips. The double‐crystal machine could sense strains as small as 10−6, with a spatial resolution of a few micrometers. Results indicate that two types of strain are present: local surface strain as well as the more familiar strain due to bulk deformation of the crystal. Both types of strain have been correlated with surface mobility changes inn‐channel metal‐oxide‐semiconductor (nMOS) transistors.