We have used electric-field-induced Raman scattering to quantitatively assess the effects of carrier screening on the average electric fields in a GaAs-basedp–i–nnanostructure semiconductor under subpicosecond laser photoexcitation. Our experimental results demonstrated that the effects of carrier screening on the average electric field were negligible for a photoexcited electron–hole pair density ofn⩽1015cm−3. As the density of photoexcited carriers increased, we observed a significant decrease of the average electric field. In particular, forn=1018cm−3, a decrease of electric field of about 50&percent; was found. All of these experimental results were explained by ensemble Monte Carlo simulations and very good agreement has been obtained. ©1997 American Institute of Physics.