The strain state of Si1‐xGex/SiO2 dummy structures on FDSOI wafers is non‐destructively characterized by HRXRD reciprocal space mapping. A transition from biaxial to uniaxial strain is detected on narrow condensed Si1‐xGex lines with shallow trench isolation (STI), revealing an increasing in‐plane elastic strain relaxation perpendicular to the trenches with decreasing line width, but no strain relaxation parallel to the trenches. The degree of crystallinity of Si1‐xGex lines degrades with increasing annealing temperature and time. An additional elastic strain reduction appears in the direction parallel to the STI trenches after deposition of source‐drain Si1‐yGey islands between dummy gates. The separation of the Si1‐xGex peaks from Si1‐yGey remains unresolved if x and y are close to each other.