Methods of forming a patterned, silicon-enriched developable antireflective material. One such method comprises forming a silicon-enriched developable antireflective composition. The silicon-enriched developable antireflective composition comprises a silicon-enriched polymer and a crosslinking agent. The silicon-enriched polymer and the crosslinking agent are reacted to form a silicon-enriched developable antireflective material that is insoluble and has at least one acid-sensitive moiety. A positive-tone photosensitive material, such as a positive-tone photoresist, is formed over the silicon-enriched developable antireflective material and regions thereof are exposed to radiation. The exposed regions of the positive-tone photosensitive material and underlying regions of the silicon-enriched developable antireflective material are removed. Additional methods are disclosed, as are semiconductor device structures including a silicon-enriched developable antireflective material.