The metal–insulator–silicon light-emitting diode (MIS LED) using a high-dielectric-constant material (HfO2) is studied. The external quantum efficiency for light emission at room temperature from the MIS LED was observed to be 2.0×10-6, as compared to 0.5×10-6 for the metal–oxide–silicon (MOS) LED. The large hole concentration at the Si/HfO2 interface created by the high dielectric constant of HfO2 may be responsible for the enhancement. The emission line shape of the MIS LED can be fitted by the electron-hole plasma recombination model, similar to the MOS LED. The Al/HfO2/silicon LED with a high interface trap density has a continuous spectrum below the Si gap beside the electron-hole plasma emission, probably due to the radiative recombination between the electrons and holes via the interface states. © 2004 American Institute of Physics.