In this study, we prepared organic-inorganic hybrid nanoparticles with a core-shell structure using a surfaceinitiated polymerization technique. Initiators for the atom transfer radical polymerization were anchored onto the surface of silica nanoparticles, and from there N-isopropylacrylamide and methylene bisacrylamide were polymerized to form cross-linked polymeric shell layers. The thickness of the polymer layers was controlled by varying the reaction time. The thermal phase transition of the surface polymer layer was characterized by dynamic light scattering analysis, which showed reversible swelling/deswelling behavior between 25 oC and 40 oC. Compared to the silica nanoparticles with linear polymer layers, the swelling/deswelling behavior was of a smaller degree, but it consistently exhibited similar size changes after repeated processes. HF etching of the silica nanoparticles with surface cross-linked polymer layers removed the silica core to render a hollow structure.