An electroluminescent device with a P-N junction capable of emitting electromagnetic radiation and with a negative resistance characteristic is formed in a III-V compound semiconductor such as gallium phosphide or gallium arseno-phosphide, the device including across its current path a current impeding portion with a small concentration of less than 5 X 1015 free charge carriers per cm.3, the arrangement being such that the current impeding action of the portion is reduced to a greater extent by radiation emitted by the P-N junction than by minority charge carrier interaction between the portion and the P-N junction.