Two-dimensional photonic band gap structures were fabricated by x-ray lithography combined with, ion etching on metalorganic chemical vapor deposition grown GaAs/AlGaAs waveguides. Such structures, more amenable to fabrication than fully three-dimensional photonic crystals, allow the confinement of light in the third direction using index guiding. The feasibility of complex high-resolution (down to 50 nm) unit cell fabrication has been demonstrated by exploiting x-ray diffraction and nonlinear resist response during the development process. Optical characterizations of some samples were performed. These characterizations show the presence of well-defined photonic band gap structures and second harmonic property generation. The results have been discussed and compared with theoretical simulation. (C) 2003 American Vacuum Society.