We report on the growth of non-cubic gadolinium oxide on a silicon substrate using molecular beam epitaxy. Structural investigations with X-ray diffraction show that the structure of the oxide differs from the expected cubic structure. Possible structures of gadolinium oxide besides the only stable cubic structure include a monoclinic and a hexagonal phase. Both phases are very similar, which increases the difficulty to distinguish between the two structures. Gracing incidence X-ray diffraction results of the grown layer indicate a monoclinic structure while in contradiction to that a phi-scan shows a sixfold symmetry. We explain these results by a monoclinic structure with six rotational domains. (C) 2017 Elsevier B.V. All rights reserved.