We studied the effect of group V switching times on the formation of interfacial layers in InGaP/GaAs heterostructures grown by LP-MOCVD using low temperature photoluminescence (PL), double crystal X-ray diffraction (DCXRD) and high resolution transmission electron microscopy (HRTEM). Due to the severe substitution process of P by As, the quality of InGaP-to-GaAs interface was very sensitive to switching times. By optimizing the switching conditions, we were able to minimize the interfacial layers to one monolayer (ML) of In Ga As at the GaAs-to-InGaP interface and 1 ML of In Ga P As at the InGaP-to-GaAs interface. Heterojunction bipolar transistors (HBTs) grown using this switching scheme showed excellent etch selectivity as well as dc characteristics.