This book is presented in five chapters. A brief summery of these chapters is given below: Chapter one exhibits a brief introduction of porous silicon and carbon nanotubes: Chapter two presents a review of the techniques that employed to produce porous silicon nanostructures and embedding multi wall carbon nanotubes to enhanced the characteristics of porous silicon photodetectors: Chapter three describes the experimental work and presents all instruments and devices employed in this work: Chapter four presents the results and discussions of the surface morphology, chemical, optical and electrical properties of porous silicon before and after embedding multi wall carbon nanotubes: Finally, chapter five presents the conclusion and the suggested future work.