GaAs/Al(x)Ga1-xAs (x=0.5, 0.6, 1.0) superlattices used as buffer layers in high electron mobility transistors and photomultiplier devices can smooth out interface roughness. The mechanism of the smoothing effect has been discussed in detail. The initial stage of nucleation on the substrates has been clearly verified by examining the undulations of a 30 nm GaAs layer sandwiched between the substrate and the superlattice.