In the last few years, great efforts have been spent in the development of integrated microsystems, devices of few square centimeters in size including microsensors, microfluidic components, reaction chambers, detectors, and so on. More than a simple ensemble of devices, this is a new research field that combines the properties and characteristics of different materials to find innovative and affordable solutions in applications such as sensing, biotechnology, analytical chemistry. The device miniaturization not only means lower costs through mass production, but also improvement in terms of analysis time, simplicity of use and decrease in consumption of materials (reagents and analytes)(Chandrasekaran et al., 2007). The integrated devices are largely made of silicon but can also include a microfluidic systems; for this reason, their technology is based both on the techniques used in integrated circuit manufacturing and on “soft” fabrication methods (Xia & Whitesides, 1998). In this chapter, we describe the fabrication and the characterization of integrated photonic devices based on nanostructured silicon for biochemical optical sensing. The porous silicon (PSi) is fabricated by electrochemical etching of doped crystalline silicon in an aqueous solution of hydrofluoridric acid. It can be simply described as a network of air holes in a silicon matrix: its dielectric properties, and in particular the refractive index, depend on the content of void, which can be accurately controlled by tuning the process parameters, so that different structures (Fabry-Perot interferometer, Bragg mirror, optical microcavity, aperiodic multilayered sequences) showing good quality …