The term "kinetic segregation" is applied where the kinetics of an alloy crystal growth process induce segregation although the homogeneous mixture is the equilibrium state. MBE growth of GaAlAs on 〈110〉 surfaces has been observed to exhibit such kinetic segregation. An explanation of kinetic segregation is offered in terms of the release of energy, approximately the cohesive energy, when an atom attaches to a kink site on a growth step of the growth surface. It is asserted that for a time τ until this energy is dissipated another atom cannot attach at that kink site. Because more energy is released by Al than by Ga atoms, Al expels Ga from kink sites longer than vice versa. The kinetic segregation is derived from this asymmetry. τ is deduced to be 10-7 s. © 1985.