X-ray diffraction topography method was employed in order to observe in situ the melting of silicon, attention being focused on the dislocation effect on the shape of crystal-melt interface. In the case of low dislocation density, the melting took place uniformly, and the shape of crystal-melt interface was flat. In the case of high dislocation density, inhomogeneous melting was observed. Therefore, the shape of crystal-melt interface was not flat. The inhomogeneous melting must be related to the existence of large amount of dislocations induced by the thermal stress.