A new Monte Carlo method has been developed for simulating backscattered electron spectra, and this was applied for determining the surface excitation parameter (SEP). The simulation is based on direct tracking of electron trajectories in the solid, taking into account elastic and inelastic events. The elastic scattering cross sections are taken from literature, while inelastic cross section data are obtained by a fitting procedure. After some iterations, the program produces electron spectra fitting well to the experimental ones. Si and Ge electron spectra were simulated and SEP values were calculated. The SEP values are compared to other ones from literature.