An adequate emitter shape for a gas field ion source was investigated to obtain a higher angular current density, dI/d. Single-crystalline << 111 >>-oriented tungsten emitters having a similar tip radius of curvature and a different taper angle of emitter shank were prepared by dc- and ac-electrochemical polishing. The tip apex of the emitters was terminated with a tungsten trimer by means of remolding and a field evaporation processes. The helium ion currents emitted from these trimers were measured as a function of helium pressure. The ion current and the dI/d obtained from the emitter with a taper angle of 1.5 degrees were enhanced by factors of 2.7 and of 3.9, respectively, compared to those from an emitter with a taper angle of 14.5 degrees. These experimental results suggest that to obtain a higher dI/d, the emitter having a narrower taper angle is better.