The structure and the rheological properties of thermoplastic elastomer gels composed of polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock copolymer (SBM) in a selective solvent for the midblock have been investigated over a wide range of concentrations. At low polymer concentration, the S and M endblocks are mixed into spherical microdomains and SBM gels behave like ordinary ABA triblocks. At sufficiently large polymer concentration, S and M are segregated in distinct cylindrical or lamellar microdomains dispersed in an elastomer matrix comprising the B midblocks swollen with the solvent. The low-frequency storage modulus significantly increases upon demixing. Hence, under appropriate conditions, the presence of two different endblocks in ABC copolymers can promote bridge formation and lead to elastomer gels with improved mechanical performance.