Although many researches using nonthermal and thermal models have been conducted on ultrashort pulse laser processing, a promising tool for precision fabrication, an understanding of the underlying mechanism is still needed. The present study, in which molecular dynamics was carried out, accepted a thermal aspect as Tersoff model for silicon does not consider the nonthermal effect due to the electron-hole density. The kinetics of melting from the molecular motions was investigated by Voronoi polyhedron (VP) analysis as a structural tool. The results have shown that the ultrafast melting by the laser with 100 fs pulse is governed by bulk melting homogeneous nucleation. The bulk melting characteristics were revealed in the absence of liquid-solid interface, a melting speed excessively higher than the speed of sound, and kinetics consistent with that of the thermal model on homogeneous nucleation.