High quality GaAs films with dislocation densities of less than 1×106cm−2on (100) Si substrates have been obtained by selective area growth using the metalorganic chemical vapor deposition method. Remarkable reduction of residual stress and dislocation density in the GaAs layers due to selective area growth have been analyzed using a simple model, in which the assumptions are that the generation of dislocations is caused by thermal stress in the films and dislocation density reduction in GaAs films on Si due to selective growth is caused by stress relief.