A focused ion beam (FIB) has been used for Si submicron device fabrication.p‐njunctions and two terminal resistors were fabricated using a 60 keV Ga+ion beam of diameter as small as 0.2 μm. Typical resistor dimensions were 50–160 μm in length and 0.2–0.5 μm in width. The Ga+dose ranged from 5E13 to 5E14 Ga/cm2.I–Vmeasurements showed the correct dependence of resistance on resistor length, width, and impurity concentration. We have studied the broadening of lines implanted in Si and SiO2using a fixed ion beam diameter as a function of dose level. Selective etch (H3PO3at 180 °C for Si and HF for SiO2) and SEM analysis showed an increase of 50%–75% in linewidth as the dose was increased by an order of magnitude.