The dewetting process of an ultrathin film of a triblock copolymer, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was studied with an atomic force microscope. The surface morphology of the dewetting process exhibited two distinct dewetting processes of the 5.6 nm thick films: a slower dewetting for the polymer layer at the very vicinity of the substrate's surface, and a faster one for the polymer on top of this layer. The surface-induced difference in the kinetics of these two-step dewetting processes resulted in a special morphology evolution, including the absence of the dewetting rim, and a final unique network-like morphology.