The present invention intends to provide a light-emitting transistor (LEFET), a light-emitting device with a switching function, which can produce an adequately strong emission of light with higher emission efficiency. The drain electrode 25 is made of aluminum and the source electrode 24 is made of gold. When a voltage is applied between the source electrode 24 and the drain electrode 25, the source electrodes 24 and the drain electrodes 25 inject positive holes and electrons into the light-emitter layer 26, respectively. The positive holes and the electrons recombine, whereby the light-emitter layer 26 generates light. The on/off state of the emission can be controlled by switching the gate voltage on and off. In contrast to conventional LEFETs in which the drain electrode is also made of gold, the present invention uses aluminum, whose work function is lower than that of gold, whereby a larger number of electrons is injected into the light-emitter layer 26 at a lower voltage. Therefore, both the emission strength and the emission efficiency are improved.