Modification of HD-PE with high energy electrons is well known and used to change the properties by cross-linking. For industrial applications like heat shrinkable films, tubes and thermostable pipes, HD-PE is usually irradiated at ambient conditions in the solid state. Due to limited mobility of macromolecules in the crystalline phase, chemical reactions of irradiation-induced radicals will occur mainly in the amorphous phase and at the interface between crystalline and amorphous phase. In contrast to the state of art technology at stationary conditions, the electron-induced reactive processing (EIReP) combines the electron modification with melt mixing. Chemical reactions are induced by spatial and temporal precise input via high energy electrons under dynamic conditions in the molten state. In the present study, the effect of these different procedures on morphology and structural properties of HD-PE has been investigated as a function of absorbed dose by using optical microscopy equipped with a hot stage and transmission electron microscopy as well as X-Ray analysis and differential scanning calorimetry.