The focused beam size and current for a JBX 5DII electron beam lithography system was measured for various shaped, (100) single‐crystal LaB6cathodes at 50‐kV beam voltage. The performance of a 90° full angle, conically shaped cathode with a 15‐μm spherical apex radius was compared with a similar cathode, but with a variable diameter flat at the cathode apex. As the flat size varied from 15 to 30 μm, the minimum beam size (for 50 pA of beam current) varied from 11 to 37 nm for a cathode temperature of 1830 K. The performance of the 15‐μm truncated compared favorably with the 15‐μm spherical shaped cathode. For larger beam diameters, the beam current for the truncated cathode exceeded that of the 15‐μm spherical shaped emitter. The truncated cathode was operated in excess of 3100 h with no performance degradation.