Porosity superlattices (SLs) are a new type of Si-based heterostructures which exhibit a periodical variation of the porosity in depth. These structures have been investigated by transmission electron microscopy. Different formation techniques for porous Si SLs will be presented : SLs on p-type doped Si were formed by periodic variation of the formation current density or by using periodically doped Si substrate layers. An influence of the substrate quality on the interface roughness has been found. On n-type Si the illumination intensity has been periodically changed during the etching process which leads to a periodical variation in the macropore radii. An explanation for this dependence is suggested.