Abstract: An improved, high strength extensible crane boom is provided which has a plurality of elongated, tubular, telescopically interfitted, longitudinally bowed, prestressed boom sections, along with a low cost method of fabricating the respective boom sections. Each boom section preferably includes an elongated upper plate having a channel structure welded to the underside thereof to form a polygonal body; permanent bowing of the body is accomplished as an incident to the welding sequence by virtue of asymmetrical heating and subsequent cooling of the metallic boom components. The boom sections are advantageously pentagonal in cross section, and the separate sides of the channel structures are simultaneously welded to the upper plates to evenly heat the plates and minimize torsional distortion of the sections.