Registration accuracy, as well as resolution capability, is one of the critical factors to identify an appropriate lithography tool. For deep submicron devices represented by the 256 Mbit dynamic random access memory, an alignment accuracy of better than 30 nm is needed. In this article, the alignment accuracy of an x‐ray stepper was evaluated using the double‐exposure method with a posiresist. The alignment accuracy obtained was better than 38 nm (3σ). Moreover, making a quantitative analysis of alignment error factors, we identified the possibility of improvement toward better than 30 nm (3σ).