We have studied the heterointerfaces of single quantum wells (SQWs) and the characteristics of SQW lasers on Si grown with Al0.5Ga0.5As/Al0.55Ga0.45P intermediate layers (AlGaAs/AlGaP ILs) by the metalorganic chemical vapor deposition (MOCVD) technique, and compare them with those grown by the two-step growth technique. The surface morphology and the heterointerfaces of SQWs on Si substrates grown with AlGaAs/AlGaP ILs are smoother than those of the two-step-grown sample. This is caused by the two-dimensional growth of the AlGaAs/AlGaP ILs. Thermal cycle annealing is found to reduce the propagation of the dislocations into the GaAs layers on Si. Excellent lasting characteristics are obtained by the AlGaAs/AlGaP ILs, which are caused by the smooth heterointerfaces. It is shown that the AlGaAs/AlGaP ILs have played an important role in achieving smooth heterointerfaces and the excellent characteristics of the SQW laser on a Si substrate.