A composite panel having a first skin forming the outer wall of the panel, known as the lower face (1), and a second skin forming part of the inner wall of the panel. The second skin is formed hollow such as to produce an inner reinforcing frame (2) in the form of a half-box structure (3) which, together with the first skin, forms box parts. The aforementioned frame is equipped with a rim (4a, 4b) for fixing to the first skin, a face known as the upper face (5) and connecting side walls (6, 6a, 6b, 6c, 6d, 6e, 7) between the rim (4a, 4b) and the upper face (5) the first and second skins forming a monolithic self-stiffened panel. The half-box frame (2) has perforated sections (8) which are defined by hollow beam sections forming the half-box frame (2).