The arrangement of a polar twin structure in Czochralski grown alpha-SrB4O7 crystals has been investigated. The transversal twin boundaries are stretched along [1 0 1] and [1 0 0] directions. The lateral twin boundaries are parallel to (0 1 0) plane. The twin structures have an extension up to centimeter size in all directions. Supposedly, they originate from polysynthetic polar microtwins revealed to form in (1 0 (1) over bar) and ((1) over bar 0 (1) over bar) growth pyramids. The dimensions, planarity and thickness stability of each individual twin are favorable for organizing quasi-phase matching conditions for nonlinear optical doubling of high-aperture beams. (C) 2015 Elsevier B.V. All rights reserved.