Light-emitting properties of devices fabricated from a copolymer of p-phenylenevinylene derivatives, 98% 3-[4′-(3,7-dimethyloctyloxy)phenylene]-p-phenylenevinylene and 2% 2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene (MEH–PV), were investigated. The emission efficiency of the devices showed strong oscillatory dependence on the film thickness, and the frequency agreed with that expected from a localized emission near the indium–tin–oxide (ITO) electrode. Although holes are injected from the ITO electrode into the copolymer layer, they are probably trapped by the MEH–PV unit of the copolymer. On the other hand, electrons are easily transported through the copolymer layer. These are probably the reasons for the confinement of the light-emitting zone near the ITO/copolymer interface. The confined light-emitting zone leads to high emission. For comparison, the properties of devices based on a homopolymer were examined. In this case, the emission zone was distributed over a wide region, and the light-emission efficiency was low. © 2001 American Institute of Physics.