The structure of a polycrystalline sample of SrOsO3 has been investigated using powder neutron diffraction from 5 to 300K, and powder synchrotron X-ray diffraction from 80 to 870K. At low temperatures SrOsO3 is orthorhombic in Pbnm and heating results in a sequence of phase transition transitions Pbnm→Imma→I4/mcm→Pm3̅m. This behavior is compared to that of other Sr containing perovskites. Comparison of the transition temperatures in SrBO3 perovskites shows that the tolerance factor alone does not determine the temperature at which the cubic phase is stabilized but rather the electronic configuration of the B-site cation appears to be significant.