High-pressure crystallized poly(ethylene terephthalate) samples were investigated with differential scanning calorimetry and scanning electron microscopy. Poly(ethylene terephthalate) (PET) extended-chain crystals with thickness up to 6 mu m were formed under high pressure. Calorimetric measurements showed that the highest melting point of these samples was 553.13 K without superheating, and the melting enthalpy was up to 138.2 J/g, higher than the value of ideal PET perfect crystals used by some researchers.