Atomic layer intermixing at pseudomorphic interfaces has been evaluated directly by changing of electronic states due to disordering in (GaAs)(m)(GaP)(1) (m = 2, 3, 4) superlattice grown by atomic layer epitaxy (ALE). The results show the critical change of the electronic structures due to atomic layer intermixing at GaAs/GaP hetero interface. The interdiffusion coefficients are about two orders of magnitude higher than values of the self-diffusion. It is suggested that microscopic and inhomogeneous strain effects are closely related to the exchange of neighboring atoms at the interface.