We have measured the photoreflectance (PR) spectrum at 300 K from a lattice-matched InP/InGaAs heterojunction bipolar transistor structure grown by gas-source molecular beam epitaxy. From the observed Franz-Keldysh oscillations we have evaluated the built-in dc electric fields and associated doping profiles in the n-InGaAs collector and n-InP emitter regions. These donor concentrations are in agreement with capacitance-voltage and secondary ion mass spectroscopy determinations, but are considerably lower than the intended values from the growth parameters. We have thereby detected a failure of the Si doping source which occurred during material growth using this contactless, nondestructive, and rapid characterization method. The energy of the InGaAs band gap from the PR spectrum also verifies the lattice-matched nature of the system, further demonstrating the diagnostic and process control value of the PR technique.