Thermal fractionations performed using differential scanning calorimetry (DSC) to characterize the heterogeneities in molecular structures of low-density polyethylene (LDPE), silane-grafted LDPE (G-LDPE), and silane-grafted water-crosslinked LDPE with gel fractions of 30 and 70 wt % are reported. In regular DSC analyses, LDPE, G-LDPE, and the low gel fraction of crosslinked samples (30 wt %) give one broad endothermic peak at similar to 110 degreesC, whereas the high gel fraction of crosslinked samples (70 wt %) give overlapped multiple endothermic peaks in a much broader temperature range. After thermally fractionated in the range 60-145 degreesC, LDPE, G-LDPE, and the low gel fraction samples give five to six endothermic peaks in the low-temperature range, whereas the high gel fraction samples give nine peaks, with three additional peaks appearing in the high-temperature range. These multiple peaks correspond to fractions of different molecular structures, with the additional peaks for the high gel fraction samples corresponding to the fraction of molecular segments with low or no branching. This fraction of molecular segments is increasingly extruded out of the gel region with increasing gel fraction by crosslinking and leads to an enhancement of crystallization of the sample. This crystallization enhancement behavior is also demonstrated by the X-ray diffraction data and polarized optical micrographs.