The stable phase that forms near 2:2:1 in the Bi‐Sr‐Cu oxide system is now recognized as a semiconducting phase structurally distinct from the n = 1 Bi‐cuprate superconductor, whose actual composition (Bi2Sr2‐xCuO6‐y, x= 0.1‐0.25, y=0‐0.5) is deficient in Sr. The 2:2:1 phase forms by a slow solid‐state replacement of the superconducting phase for compositions near 2:2:1. It also can be grown from melt compositions involving several phase assemblages, but single‐phase products are not obtained, implying incongruent melting. Alumina and zirconia crucibles promote the growth of the superconducting phase by reacting with the melt to remove Sr, whereas Au crucibles promote the growth of the 2:2:1 phase. Owing to its fine‐grained, fibrous habit, structural characterization has been difficult. Of the unit cells proposed, the C‐centered monoclinic cell of Roth et al. provides the best fit to our x‐ray powder and single‐crystal precession data, a = 24.522(9), b = 5.426(2), c = 21.983(9) Å, β = 105.00(3)°. Perfect prismatic cleavages intersecting at ‐148° and ‐32° are indexed as {100} and {‐201} forms. Although, the superconducting n = 1 Bi‐cuprate exhibits variable Sr and O contents, the 2:2:1 phase appears to be a single composition with no oxygen exchange observed by TGA, although it may be somewhat deficient in Cu. The 2:2:1 phase is semiconducting as determined by electrical resistivity measurements, with an apparent activation energy of 0.013 eV. For a 2:2:1 stoichiometry, the measured density of ‐7.2. g/cm3 implies 16 formula units per cell.