High-power illumination of a p-i-n photodiode results in nonlinear operating conditions and, of course, in nonlinear electric response. This article presents an investigation and comparison of the nonlinear response of conventional and resonant cavity enhanced (RCE) p-i-n photodiodes constructed using a two-valley semiconductor (GaAs). The presented results are obtained through numerical simulation of the complete phenomenological model for a two-valley semiconductor in the submicron region for several bias voltages and several values of Dirac pulse optical powers. The nonlinear behavior is analyzed through carrier transit and response time. Nonstationary effects exist in two-valley semiconductors in the presence of adequate perturbation of the electric field in the absorption layer. The present investigation shows that the RCE p-i-n photodiode reaches the nonlinear operating regime for smaller incident optical irradiances.