Abstract: The invention relates to a method for embossing a channel structure (3) comprising a plurality of parallel channel portions (5) in a planar metal sheet (11) to form a half-plate (2, 2?), in particular for a bipolar plate (1) of an electrochemical cell, said method having the following steps: providing the planar metal sheet (11) with a uniform initial wall thickness (d5), inserting the metal sheet (11) into a forming tool (12), wherein a base plane (BE) of the sheet (11) defined by the undeformed planar metal sheet (11) is provided to rest on a tool plane defined by a tool part (13) of the forming tool (12), forming the plurality of channel portions (5), each channel portion (5) being designed with two non-parallel flanks (7, 8) in such a way as to allow material from embossing portions (9, 10) of the metal sheet (11), which are located outside the flanks and remain in the base plane (BE) and/or a plane parallel thereto throughout the entire forming process, to be displaced into the flanks (7, 8), each fla