Abstract Depending on the composition of  oriented short period Si mGe n superlattices (m monolayers Si/n monolayers Ge) there are six different space groups. In case of m+n odd the microscopic periodicity is doubled to 2(m+n) monolayers due to the tetrahedral bonding. We prepared several superlattices namely Si 2Ge 3, Si 3Ge 3 and Si 4Ge 6 with low temperature molecular beam epitaxy. Using selected area diffraction in the transmission electron microscope we found the microscopic periodicity of 10 monolayers for Si 2Ge 3 and Si 4Ge 6. For Si 3Ge 3 the vertical periodicity is six monolayers.