N-type semiconductors A N-type semiconductor is an intrinsic semiconductor (e.g. silicon Si) in which a donor impurity (e.g. arsenic As in Si, or Si in GaAs) has been intentionally introduced. The impurities are called donor impurities since they have to give an extra electron to the conduction band in order to make all the bonds with neighboring atoms (As is pentavalent while Si is tetravalent).