The semiconductors have energy gap separates the electron energy levels that are normally filled with electrons from those that are empty of electrons. Si, SiC and GaN have bond strengths suitable for high-temperature applications. Porous Si, SiC and GaN can be formed by photo-electro-chemical etching and those have unique properties and applications as electro-optical devices, fuel cells, sensors and actuators. The book presents for both experts and non-experts the knowledge and applications of porous materials having average and wide band gap. The book starts with an overview of porous Si includes preparation, characterization and morphology of Si solar cells. Followed by mechanism of porous SiC formation, and describe biological applications of porous SiC. Finally, produce porous GaN for different applications. This book is aimed to achieve work relating to porous semiconductors for manufacturing and technology. It is very appropriate for post-graduates, researchers and academicians in Nanotechnology and Nanoscience.