Reported here is the thermotropic behavior of cationic gemini/phospholipid/DNA complexes investigated by synchrotron X-ray diffraction. At low temperature, DNA forms rectangular columnar superlattices between interdigitated bilayers. At temperatures above the lipid main phase transition, the transbilayer DNA ordering is partly preserved and DNA arranged into a simple rectangular lattice. This is the first time that such a predicted superstructure is observed in the liquid-crystalline phase of cationic lipid/DNA complexes.