A novel carbon allotrope consisting of parallel zigzag and armchair chains alternatively each other (10 atoms/cell, named pza-C-10) was discovered. The calculated band gap of pza-C-10 is 0.31 (0.71) eV with PBE (HSE06), and thus the new member of carbon family is a semiconductor. The pza-C-10 sheet not only is thermodynamically more stable than the other known semiconducting carbon sheets, but also it can perfectly graft with graphene. The unprecedented properties of pza-C-10 provide a new approach of modulating intrinsic band gap through forming graphene-based monolayer carbon superlattices (GSLs). The band gaps of GSLs with zigzag type of interface oscillate between semiconducting and semimetallic (mostly at the Dirac point) states as the number of zigzag chains increases, showing quantum size effect. The 2D superlattice achieved in GSLs opens a new strategy to design the crystal structures and modulate the electronic properties of 2D materials, nanoribbons, and nanotubes.