Direct measurements of electron and hole leakage over the heterobarrier in In-GaAsP/InP lasers are carried out by using a novel laser-bipolar-transistor structure. Experimental results indicate a significant amount of electron leakage under normal laser operating conditions

while hole leakage is found to be negligible. The electron leakage increases continuously with increasing injection

and is sensitive to the ambient temperature. By elimi-lating the electron leakage

an increase of about 30K in the characteristic temperature T0 is possible. The experimental observations can be explained by a model which takes the electric field and carrier heating effect into account. Following this line

a new laser structure is designed and realized

resulting in a low threshold current （-20mA） and a reasonable high T0 （-90K）.