Electron‐electron scattering of ballistic electrons in a two‐dimensional electron gas was studied as a function of the electron excess energy above the Fermi energy and of temperature. At low temperatures of 1.4 K it is found that for excess energies of approximately 30% of the Fermi energy the electrons in a ballistic electron beam are already scattered significantly due to electron‐electron interaction. A very good agreement between our experimental data and theory was found, when the measured data were compared with numerical calculations based on a theory of Giuliani and Quinn [Phys. Rev. B26, 4421 (1982)], while the agreement was only poor for the analytical approximation of the electron‐electron scattering rate. ©1995 American Institute of Physics.