AbstractThe thermal expansion of GeSe has been studied above room temperature up to the melting point of 670 ± 5°C by X‐ray diffraction techniques using a 190 mm Unicam high temperature camera. The thermal expansion of the crystallographic axes is linear with a distinct change of the expansion coeffients for all axes above 400°C. The relative changes of the axes indicate a rearrangement of the structure towards cubic symmetry with increasing temperature. The transformation of GeSe from the orthorhombic to a normal NaCl‐type structure is observed at 651 ± 5°C. The lattice parameter of the cubic form of GeSe is a0= 5.730 ± 0.003 Å at 656°C. The GeSe lattice remains cubic up to the me