Polyurethane block copolymers chemically cross-linked by pentaerythritol, a four-way cross-linker, are tested for the shape memory effect. One of the copolymers shows higher shape recovery than any other shape memory copolymer synthesized by us so far. The copolymer maintains a surprising 94% shape recovery after the third cyclic test. The four-way cross-linking by pentaerythritol and interaction between hard segments are mainly responsible for the very high shape recovery. Tensile mechanical properties also significantly improve by cross-linking. Glass transition temperature($T_g$) slightly increases with cross-linking content. Other characterization such molecular weight, IR, and X-ray diffraction is also carried out to understand the arrangement of copolymer chains.