Geiger–Müller counters are widely used to detect ionizing radiation by measuring electrical discharges within a gas-filled chamber. In this project, we aim to miniaturize this principle using microfabrication techniques, replacing the conventional gas chamber with a microscale structure. The approach involves fabricating high aspect-ratio silicon pillars, coated with a conductive aluminum layer and embedded within an insulating polyimide matrix. The entire fabrication process was performed in the CMi cleanroom at EPFL, following a predefined process flow that was refined to optimize critical fabrication steps. By the end of this project, a functional microsystem was successfully fabricated. The final device consists of silicon pillars of 4 μm diameter (see figure 2), coated with 5 μm of aluminum, embedded in a 10 μm-thick polyimide layer, and covered by a 1 μm aluminum counter-electrode. Figure 1a shows the final structure.