Metallurgy and inorganic chemistry quickly blends into condensed matter physics.

Metals and semiconductors will arrange themselves in specific crystal structures that depend on their electron valence. In the crystal the outermost electrons tend to get shared collectively. What that looks like is the energy levels that once belonged to the discrete atoms blend together to form bands. The band that corresponds to the original valence orbitals is called the valence band, and the next higher the conduction band.

The difference between metals and semiconductors is in the latter there is an energy gap between the bands, where in a metal the band energies meet at specific points in the crystal. Think of them as two sets of roads, local streets and a highway system. In a metal there are plenty of on-ramps and the electrons can move all about the crystal.

In a semiconductor there are no on-ramps, so the local streets are totally log-jammed and electrons stay stuck in place. If you manage get rid of a valence bad electron (e.g. thermally kick it up to the conduction band) there is now a little wiggle room and electrons can hop from atom to atom in the crystal.

TL,DR its sort of like covalent bonds, but instead of molecular orbitals they are really big