We investigate the structure and thermal stability of freestanding SiGe/Si rolled-up microtubes by secondary ion mass spectroscopy, scanning and transmission electron microscopy, as well as micro-Raman spectroscopy. The tube walls show good crystal quality but become thinner during tube fabrication, leading to smaller diameters than expected. Si–Si vibration modes from the wall are consistent with Raman shifts induced by the strain distribution in the structure. Furthermore, the Raman shifts are used to monitor the tube temperature during laser annealing. At high temperatures, the tube structure irreversibly changes due to Si and Ge interdiffusion and, most remarkably, by Ge condensation.