The present disclosure provide a method for using a hard mask layer on a top surface of fin structures to form a fin-top mask layer. The fin-top mask layer can function as an etch stop for subsequent processes. Using the fin-top hard mask layer allows a thinner conformal dielectric layer to be used to protect semiconductor fins during the subsequent process, such as during etching of sacrificial gate electrode layer. Using a thinner conformal dielectric layer can reduce the pitch of fins, particularly for input/output devices.