A method for forming a distributed Bragg mirror on a quantum cascade laser, comprising: - providing a stack of layers based on materials III-V comprising at least one active region for emitting a monochromatic light radiation, - depositing a first masking layer onto said stack , - forming first patterns in the first masking layer , - forming first trenches in the stack , at a first depth D1, from the first masking patterns , said first trenches mainly extending along a first direction (x) and being intended to form structures of the distributed Bragg mirror , - depositing a second masking layer at least into the first trenches , - forming second patterns in the second masking layer , on either side of the first patterns , - forming second trenches in the stack , at a second depth D2 greater than the first depth D1, from the second masking patterns , said second trenches mainly extending along a second direction (y) perpendicular to the first direction (x) and being intended to form walls of the quantum cascade laser, - removing the second masking layer from the first trenches , - filling said first trenches with at least one metal material, said method being characterised in that it further comprises: - before depositing the second masking layer , forming a sacrificial interlayer at least in the first trenches , and - before filling said first trenches with at least one metal material and after removing the second masking layer from the first trenches , removing said sacrificial interlayer so as to remove by lifting off residues of the second masking layer remaining in the first trenches at the end of the step of removing the second masking layer from the first trenches . - providing a stack of layers based on materials III-V comprising at least one active region for emitting a monochromatic light radiation, - depositing a first masking layer onto said stack , - forming first patterns in the first masking layer , - forming first trenches in the stack , at a first depth D1, from the first masking patterns , said first trenches mainly extending along a first direction (x) and being intended to form structures of the distributed Bragg mirror , - depositing a second masking layer at least into the first trenches , - forming second patterns in the second masking layer , on either side of the first patterns , - forming second trenches in the stack , at a second depth D2 greater than the first depth D1, from the second masking patterns , said second trenches mainly extending along a second direction (y) perpendicular to the first direction (x) and being intended to form walls of the quantum cascade laser, - removing the second masking layer from the first trenches , - filling said first trenches with at least one metal material, - before depositing the second masking layer , forming a sacrificial interlayer at least in the first trenches , and - before filling said first trenches with at least one metal material and after removing the second masking layer from the first trenches , removing said sacrificial interlayer so as to remove by lifting off residues of the second masking layer remaining in the first trenches at the end of the step of removing the second masking layer from the first trenches . <EOS>