A single cavity mode optoelectronic device, such as a VCSEL, an RCLED or a DFB laser diode, comprises an etched-pillar or mesa structure including an optically active region and strain-applying means in the form of a layer of polymer material having a coefficient of thermal expansion which is greater than that of the optically active region. The layer surrounds the optically active region so as to apply a compressive strain to the latter so as to compensate at least partially for temperature-induced changes in the gain spectrum peak of the optically active region caused by ohmic heating of the device.