Photoreflectance measurements of a GaAs p‐i‐n diode as a function of temperature (50–450 K) are reported. The photovoltage in the structure is obtained from the electric field strength which is determined from the Franz–Keldysh oscillations in the photoreflectance spectrum. The results are compared to those from an n‐GaAs structure where the Fermi level is pinned at the surface. In this case the photovoltage can be determined only by fixing the energy of the Fermi pinning level. The theoretical photovoltages are also calculated from the ideal p‐n and Schottky diode equations. This study clearly shows the importance of the photovoltage effects in the photoreflectance measurements.