Solids that are held together by covalent bonds have the highest melting points because the molecules are firmly held together in a crystal lattice. This property makes such solids poor electrical conductors since the molecules cannot move. The metallic solid tungsten has the highest melting point among the elements.
Network covalent solids have even higher melting points than covalent solids because of the bonds shared by all the atoms. Every atom shares a covalent bond with every other atom, which means there are no molecules. As such, heat energy is spread over the entire crystal, which makes it very difficult to melt.