Momentum relaxation of photo-excited carriers in GaAs was investigated using the Monte Carlo approach. A laser of 1.51 eV photon energy and 9 fs width was assumed. Simulations were performed for excitation densities ranging from 1016 cm-3 to 8 X 1017 cm-3. For nexc equals 8 X 1017 cm-3, the distribution of the carrier momentum was found to approximate a Maxwell-Boltzmann distribution 25 fs after laser excitation, which concurs with recent experimental data. The relaxation time was shown to increase with decreasing carrier density and to be shorter when the carrier-carrier scattering was treated dynamically rather than statically.