Silicon and germanium are the cornerstones of transistor technology and the mini-electronics industry. Pure silicon and germanium are poor conductors of electricity because their outer electrons are tied up in the covalent bonds of the diamondlike framework. Diamond is an insulator because it is not easy to supply enough energy to pull the covalent-bond electrons loose and permit them to conduct electricity through the crystal. Less energy is required to free the electrons in silicon, and even less is required in germanium. These atoms are larger and hold their electrons less tightly. They are not conductors in the metallic sense of the word, but are semiconductors. At low voltages they are insulators, but they begin to conduct electricity if the applied voltage is high enough. Electrical conductivity decreases as temperature increases in metals because the vibrations of the atoms make passage of electrons more difficult. This effect is overshadowed in semiconductors by the greater number of electrons that are "shaken loose" from bonds at higher temperatures; thus semiconductors become better conductors as the temperature increases.