This paper presents theoretical and experimental studies of ultrabright internal second harmonic during femtosecond superradiant emission generation in multiple sections GaAs/AlGaAs laser structures at room temperature. Experimentally measured conversion efficiencies are by 1-2 orders of magnitude greater than expected. To explain this fact, a model based on one-dimensional nonlinear Maxwell curl equations without taking into consideration the slowly-varying envelope approximation has been developed. It has been demonstrated that strong transient periodic modulation of e-h density and refraction index dramatically affects the process of superradiance in semiconductor media and can explain the ultrastrong internal second harmonic generation.