Photoellipsometry (PE), a contactless optical method, combines the features of both spectroscopic ellipsometry and photoreflectance (PR) and offers more complete information about the sample from a single experiment. PR, on the other hand, has been widely used for characterizing semiconductor microstructures. The nondestructive nature and the relatively sharper features produced in the measured spectra make this method very attractive. It was based on these advantages that we applied PE and PR to Si (delta) -doped GaAs. Two Si (delta) -doped GaAs samples were investigated in this study, each having an undoped GaAs cap layer of thickness (L equals 100 and 200 nm, respectively). Our main objective was to determine built-in electric field strength in the cap layer of each sample. In the analysis of the measured PE spectra, the Franz-Keldysh (FK) theory was used, taking into account the broadening and the photovoltage effects, whereas the measured PR spectra were analyzed using the asymptotic form of an Airy function for the FK oscillations. The results of our analysis show that, for each sample studied, the field strength obtained from PE spectra is in good agreement with that determined from PR spectra, and that the field strength decreases with the increase of the cap layer thickness.