3D Si hollow-woodpile photonic crystals are formed through the direct-write assembly of concentrated polyelectrolyte inks (rods similar to 1 mu m in diameter) followed by a sequential silica/silicon chemical vapor deposition process (see Figure). The direct conversion of 3D polymer microstructures to materials like silicon may enable such applications as photonic materials, low-cost microelectromechanical systems (MEMS), microfluidic networks for heat dissipation, and biological devices.