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Any of various solid substances, such as silicon or germanium, that conduct electricity more easily than insulators but less easily than conductors. In semiconductors, thermal energy is enough to cause a small number of electrons to escape from the valence bonds between the atoms (the valence band); they orbit instead in the higher-energy conduction band, in which they are relatively free. The resulting gaps in the valence band are called holes. Semiconductors are vital to the design of electronic components and circuitry, including transistors, laser diodes, and memory and computer processing circuits.