Abstract A resist-trimming process for the SAL601 chemically amplified negative electron beam resist has been investigated. Ultra-fine SAL601 resist patterns with a width of 16 nm were obtained through isotropic trimming of patterns produced by electron beam lithography in oxygen plasma. This pattern resolution in SAL601 could not be obtained through electron beam lithography alone. Using this trimmed electron beam resist, we have successfully fabricated ultra-fine polysilicon patterns of less than 20 nm width. It was found that this trimming process is reproducible and uniform, making it a useful process for nanometer-scale device fabrication.