A substance such as germanium or silicon whose electrical conductivity at normal temperature is usually intermediate between that of a metal and an insulator, and whose conductivity is anisotropic. Its concentration of charge carriers increases with temperature over a given range. Current flow may be by movement of electrons (n-type) or by the transfer of positive holes or missing electrons (p-type). Many common metallic sulfides and oxides are semiconductors. Their resistivity generally lies between 10–5 and 107 ohm-m. See transistors.