Microfocused heavy ion beams obtained from liquid metal ion sources of gallium, indium, and tin are bombarded onto silicon and gallium arsenide substrates, and the amorphous regions created are selectively dissolved in suitable etchants (ion bombardment enhanced etching). The area exposure doses required to etch to the depth of the calculated projected range of the incident ions are in the region of 5×10−6∼1×10−5C/cm2at accelerating voltages of 30∼50 kV,and the dose dependencies of the etched depths show rapid increases in specified dose regions. Widths of etched depths obtained in line delineations depend on a line exposure dose, and the minimum linewidth clearly obtained is 20∼40 nm for all the ion beams. From measurements of the dose dependencies of linewidth, the beam diameters are evaluated for various conditions of the source operation and of a lens acceptance half‐angle. The virtual crossover diameters that are independent of the half‐angle, are found to be 40∼50 nm for the gallium source and 67 nm for the indium source at the emission current of 4∼12 μA. In the case of the tin ion beam, each line is split into two distinct lines about 100 nm apart at 50 kV. This effect is caused by the separation of singly and doubly charged atomic ions in some stray magnetic field of the order of 50 mG. From variations of the width of grooves produced by the bombardment with the doubly charged ion beam, the crossover diameter for the tin source is estimated to be 56∼67 nm.