The common crystallization conditions of poly(ethylene terephthalate) (PET) were replaced by an anabaric high-pressure crystallization at 320 degrees C. The PET samples were characterized by differential scanning calorimetry, density and microhardness. The resulting two-phase microstructure was studied by means of absolute small-angle X-ray scattering (SAXS). A complete SAXS analysis utilizing the interface distribution function (IDF) method was carried out. The resulting structure exhibited the presence of stacks of 10 nm thick crystalline lamellae which were separated by amorphous layers of about 1.3 nm thickness. Similar structures have been found after annealing of amorphous metals and have been termed nanocrystalline. Microhardness and structure have been discussed in analogy with the notions from the field of nanostructured materials. Theoretically, a multi-component lamellar two-phase structure has been discussed. The equations derived allow the computation of volume fractions and specific surfaces of the components (different kinds of stacks).