A sidewall image transfer process for forming sub-lithographic structures employs a layer of sacrificial material that is deposited over a structure layer and covered by a cover layer. The sacrificial material layer and the cover layer are patterned with conventional resist and etched to form a sacrificial mandrel. The edges of the mandrel are oxidized or nitrided in a plasma at low temperature, after which the material layer and the cover layer are stripped, leaving sublithographic sidewalls. The sidewalls are used as hardmasks to etch sublithographic gate structures in the gate conductor layer.