A method of fabricating 40-nm gate-length n-metal-oxide-semiconductor field effect transistors (MOSFETs) is described in detail. The fabrication of MOSFETs with gate lengths of this order poses two major problems : how to fabricate such small-geometry gate electrodes, and how to fabricate the ultrashallow source and drain junctions required. Two special techniques are used to overcome these problems : a resist-thinning process using isotropic oxygen plasma ashing for the fabrication of the gate electrodes, and a process of solid-phase diffusion from phosphorus-doped silicated-glass gate sidewalls for fabrication of the source and drain junctions. The resulting 40-nm gate electrodes and ultrashallow 40-nm junctions have an adequate impurity concentration and have been shown to function successfully. It has been confirmed that these 40-nm gate-length n-MOSFETs have good electrical characteristics at room temperature, Certain details of small-geometry MOSFET electrical characteristics are studied using these devices.