In GaAs/InGaP/GaAs structures grown by metal organic vapor-phase epitaxy (MOVPE), the two heterointerfaces are not identical. Normal photoluminescence (PL) features corresponding to the band gaps of GaAs and InGaP are seen for InGaP layer grown on GaAs, However, an intense long-wavelength feature is observed if we grow GaAs on InGaP (inverted structure) while the features of InGaP and GaAs are suppressed. The nature of interfacial regions is investigated by using different gas switching sequences, which can influence the interfacial region composition. Significantly, we find anomalous PL features similar to those observed in the case of inverted structure if we briefly interrupt the growth of InGaP on GaAs and introduce AsH3 during the growth interruption. Secondary-ion mass spectrometry (SIMS) measurements and preliminary results of the compositional analysis of the interfacial layers based on high resolution X-ray diffraction (HRXRD) and PL measurements suggest that a deleterious effect arises with the exposure of InGaP surface to AsH3 and is attributed to the formation of an interfacial InGaAsP layer,