A patterning technology for fabrication of nanometer structures in Si/SiGe heterosystems is developed. The method pursued here combines high‐resolution electron‐beam lithography with reactive‐ion‐etching pattern transfer. A modified SF6/O2dry‐etching process is optimized by varying the gas mixture to achieve the required anisotropy. Photoluminescence measurements are carried out on uniformly etched samples to determine the influence of the reactive‐ion‐etching process on the optical properties. Etch process induced surface modifications drastically alter the electrical surface potentials. They are identified by laser desorption. These modifications are partially removed by low‐temperature postannealing steps. A qualitative model is presented to explain the observed effects. With this optimized technology, SiGe wires with lateral widths from 4 μm down to 25 nm are fabricated. Photoluminescence has been detected for structures as small as 600 nm.