Photoellispometry, a contactless optical method sensitive to surface and interface built-in electric fields, was applied to two types of doped semiconductor microstructures, namely, a delta-doped GaAs structure and a modulation-doped AlGaAs/GaAs heterojunction structure. The objective of this research was to use photoellipsometry for the determination of the sample’s physical properties, such as built-in electric field strength, depletion width, broadening, and bandgap energy. The measured spectra were analyzed using the Franz-Keldysh theory, which also included the effects of field inhomogeneity and broadening. Good agreement was found between the measured and calculated spectra, indicating that the theory and model used were appropriate for the samples investigated and that the calculated results were reliable. Our analysis suggests that the field was uniform in the top layer for the delta-doped GaAs samples and linearly decreasing in the top layer for the modulation-doped AlGaAs/GaAs heterojunction samples. This in turn demonstrates the effectiveness of the method in the characterization of the chosen semiconductor microstructures.