The implementation of a Mid-InfraRed (MIR) silicon photonics transducer with broad transparency (up to 8 µm) is a challenge that could find applications in spectroscopic sensing and environmental monitoring. Due to silica absorption above 3.6 µm, the conventional silicon-on-insulator platform, used in the near infrared (NIR) wavelength range, is not adapted for MIR broadband silicon photonic integrated circuits. Another approach is to use silicon-on-sapphire or silicon pedestal structures [1]. A waveguide using porous silicon (PSi) layers was also proposed for MIR devices, in which the guiding layer is a silicon layer and the waveguide cladding is a PSi layer created by high-energy proton beam irradiation and electrochemical etching [2]. However, high propagation losses were measured in these structures at 3.39 µm. Several photonic integrated circuits based on PSi were demonstrated in the NIR wavelength range [3, 4]. However, in the MIR, only PSi optical rugate filters with reflectance peaks matching specific spectral features of molecules in the region from 4 to 8 µm have been fabricated so far [5]. This work demonstrates for the first time to our knowledge, the use of an electrochemically prepared optical ridge waveguide based on PSi operating at MIR spectral region (up to 7.8 µm). The PSi layers were obtained by electrochemical anodization of p-type doped (100)-oriented silicon wafer (4-6 .cm). The electrolyte was composed of HF(50%):H2O:ethanol (7-1-2). The refractive indices and porosities of single layers were studied by reflectometry. The thickness of each porous layer (guiding and cladding) was controlled by the anodization time. The guiding (upper) and cladding (lower) layers were formed by successively applying two current densities in order to obtain porosities about 59% and 62% respectively (sample A) or about 59% and 65% respectively (sample B). Lastly, PSi waveguides (sample C) were also fabricated from p-type heavily doped (100)-oriented silicon wafer (5 m.cm). The thicknesses of the guiding and cladding layers were equal to 2.7 µm and 6 µm respectively for samples A and B. The thickness of the cladding layer was chosen to avoid radiative losses. The ridge waveguides (Figure 1a) were subsequently patterned using standard i-line photolithography and fluorine-based reactive ion etching. To demonstrate the capacity of these PSi waveguides for MIR spectroscopic sensor application (2-8µm), QCL light at 7.8 µm was coupled in a single-mode chalcogenide fiber-and injected into the waveguide. The intensity of the light at the waveguide output was collected with a MIR objective and imaged on a digital camera. MIR propagation was observed in samples A and B, whereas for sample C, no propagation was observed. The heavily doping of the silicon substrate could explained the