The bond that forms a semiconductor is a covalent bond. In a covalent bond, two or more atoms share electrons in order to achieve a stable configuration. In semiconductors, such as silicon and germanium, each atom has four valence electrons which form covalent bonds with neighboring atoms, resulting in a crystal lattice structure. This lattice structure creates a small energy gap between the valence and conduction bands, which allows some electrons to move from the valence band to the conduction band when energy is added to the system, resulting in electrical conductivity.