We have studied the gain characteristics of gain‐guided quantum well II–VI laser diodes by measuring the amplified spontaneous emission spectra under several pulsed conditions. The temperature rise during one current pulse affects the gain characteristics and theL‐Icharacteristics. The net modal gain at constant peak current increases with the pulse width. The peak gain for long pulses shows a superlinear dependence on injection current. In this case, theL‐Icurve is very steep above threshold and sometimes shows an internal quantum efficiency of more than unity. This leads to an underestimation of the internal cavity loss giving a value inconsistent with the one obtained from the gain spectra. With short pulse currents (<200 ns), the peak gain shows a weak sublinear dependence on injection current. The cavity losses obtained from the gain spectra and theL‐Icharacteristics at short pulses are consistent. As a result, we obtain the intrinsic gain characteristics of gain‐guided quantum well II–VI laser diodes. ©1996 American Institute of Physics.