Semiconductor, any of a category of crystalline solids intermediate in electrical conductivity between a conductor and an insulator. Semiconductors are employed within the manufacture of assorted sorts of electronic devices, including diodes, transistors, and integrated circuits. Such devices have found wide application thanks to their compactness, reliability, power efficiency, and low cost. As discrete components, they need found use in power devices, optical sensors, and light-weight emitters, including solid-state lasers. they need a good range of current- and voltage-handling capabilities and, more important, lend themselves to integration into complex but readily manufacturable microelectronic circuits. They are, and can be within the foreseeable future, the key elements for the bulk of electronic systems, serving communications, signal processing, computing, and control applications in both the buyer and industrial markets. Any of assorted solid substances, like silicon or germanium, that conduct electricity more easily than insulators but less easily than conductors. In semiconductors, thermal energy is enough to cause atiny low number of electrons to flee from the valence bonds between the atoms (the valence band); they orbit instead within the higher-energy conduction band, within which they're relatively free. The resulting gaps within the valence band are called holes. Semiconductors are vital to the look of electronic components and circuitry, including transistors, laser diodes, and memory and computer processing circuits. Solid-state materials are commonly grouped into three classes: insulators, semiconductors, and conductors. (At low temperatures some conductors, semiconductors, and insulators may become superconductors.) Semiconductors are the materials which have a conductivity between conductors (generally metals) and non-conductors or insulators (such ceramics). Semiconductors is compounds like gallium arsenide or pure elements, like germanium or silicon. Physics explains the theories, properties and mathematical approach governing semiconductors. Semiconductor devices can display a variety of useful properties like showing variable resistance, passing current more easily in one direction than the opposite and reacting to light and warmth. Their actual function includes the amplification of signals, switching, and energy conversion. Therefore, they find widespread use in the majority industries and also the companies that manufacture and test them are considered to be excellent indicators on the health of the economy.