We report the fabrication and characterization of the smallest near-curvature-free electrostatically actuated Ni micromechanical switches reported to date. Our smallest one, which measures 10.0 μm×4.0 μm×0.15 μm suspended over a 430 nm gap is realized by using electron beam cross-linked polymethylmethacrylate as the sacrificial layer and electroplated nickel as the main structural material. Tunnel barriers are defined via in situ formation of Al2O3 during the oxygen plasma dry release step with a metal–insulator–metal junction formed when the switch closes. The reliable curvature-free properties of these devices demonstrate low pull-in voltage drifts (≪1.5 V), even after 1 billion switching cycles. Also, they did not reveal an appreciable physical change even after being subjected to sintering treatments of 450 °C for 30 min, making them promising candidates for encapsulations. These devices have low hysteretic switching behavior (∼0.5–4.5 V), as compared with similarly fabricated switches without the barrier, which remain stuck once turned on. © 2003 American Vacuum Society.