Reflectance anisotropy spectroscopy (RAS) was used for in-situ monitoring of MOVPE growth of InGaAs/InP-heterojunction bipolar transistors (HBT). Spectra were recorded during growth of differently doped InGaAs and InP layers in order to investigate the influence of the doping type and level on the spectra. The spectra of the growing InP layers show features similar to the phosphorous rich (2 x 1)-like surface. They reveal a strong effect of the doping on the RAS-signal around 4.5 eV photon energy, corresponding to the E-0' transition of InP. This is probably due to the linear electro-optic effect at this transition. The InGaAs spectra are dominated by two prominent features around 2.3 eV and 4.0 eV. A correlation between the RAS-signal of the InGaAs layers and the doping type and level is visible at different wavelengths. Transients at different wavelengths were taken during growth, focusing the investigations on the changes in the RAS-signal occurring at the interfaces between InP, InGaAs and a quaternary InGaAsP layer. Characteristic features visible in the RAS transients during the gas switching sequences indicate the formation of interfacial layers.