We report extended studies on electroluminescence from molecularly thin semiconducting Langmuir–Blodgett films of quinquethiophene. The effect of the thickness of active layer and cathode electrode material has been investigated. From all these devices, greenish electroluminescence (visible in a dark room) has been observed with quantum efficiencies of the order of 10−3%. Even five or nine layers of Langmuir–Blodgett films yield the same luminance as thicker films. The electroluminescence spectrum showed a profile identical to the photo‐ luminescence spectrum. ©1995 American Institute of Physics.