Luminescent porous poly-Si thin films can be obtained by electrochemical etching of phosphorus-doped poly-Si films deposited by low-pressure chemical-vapor deposition, As-deposited poly-Si film has no photoluminescence but all porous poly-Si films, large area or micron-size patterns, show comparable orange-red photoluminescences to those obtained from crystal Si. High-resolution atomic force microscopy and scanning electron microscopy analyses show that all porous poly-Si films have smooth surfaces and uniform thicknesses. and are composed of Si grains (similar to 150 nm) with nanopores (similar to 20 nm) formed around the surfaces. The pores increase with anodization rimer and grow preferentially along the poly-Si grain boundaries and the Si [100] crystal directions, The evolution of the microstructure is analogous to that of the etching of a coral ball layer due to sea water.