Although the threshold of quantum well semiconductor lasers has been studied by various theoretical analysis

all of the results were not the simple analysis equation but some numerical value curves.In order to obtain the analysis equation

we do a farther study.In this paper

the threshold of single-quantum-well(SQW)

multi-quantum-well(MQW) and separate confinement hereostructure quantum-well(SCH-SQW)semiconductor lasers were analyzed.The equation for the optical gain as a function of the injected carrier density at various temperatures for undoped quantum-well were derived.Using this result

the expressions for the threshold current density of the three quantum-well semiconductor lasers were obtained.