The use of a Si0.7Ge0.3strained layer as an etch stop in silicon‐based materials is reported. The etch rates were characterized through silicon and a 60 nm Si0.7Ge0.3strained layer. The etch rate through undoped silicon was 17–20 nm/min, while the etch rate through the Si0.7Ge0.3layer was 1 nm/min. After annealing the wafer to 850 °C for 30 min, transmission electron microscopy was used to show that strain in the alloy layer was only partially relieved, and that generated misfit dislocations were confined to the strained Si0.7Ge0.3layer. The etch rate through the strained layer increased to 1.7 nm/min after this treatment, and was still perfectly functional as an etch stop.