A novel fine line patterning technique for the fabrication of submicron devices is described. It is based on local oxidation and anisotropic dry etching of an aluminum film acting as a substitutional mask. Etch selectivities greater than 4:1 between plasma oxidized and unoxidized aluminum have been observed. 1500‐A˚‐wide lines with essentially vertical walls have been achieved with this technique. These Al patterns can either be used directly in device structures or as masks for the etching of underlying layers.