A 3-terminal totally integrated demultiplexing photodiode is disclosed wherein information present simultaneously at two wavelengths can be developed into two separate currents available at the three terminals. Two quaternary n-type layers (103 and 105) of indium gallium arsenide phoshide having unequal bandgaps and each having a pn junction are separated by a layer of (104) of n-type indium phosphide. The device is oriented so as to present the incoming radiation first to the quaternary layer having the larger bandgap and then to the quaternary layer having the lower bandgap. One of the contacts (111) is attached to the top layer (106) of n-type indium phosphide, a second contact (112) is attached to a central p-type region (110) established in the top layer of indium phosphide and penetrating through to the top quaternary layer, and the third contact (113 or 302) is connected either to the indium phosphide substrate (101) or to a p-type outer region (301) that surrounds all of the layers. By reversing the dc potential applied to the junctions in the quaternary layers, a dual-wavelength light emitting diode is provided.