A testing apparatus for inspecting the beams formed by a multisource module (MSM) was built for the feasibility study of a beam splitting array (BSA), a multielectron beam system the authors are developing. In this BSA, the MSM plays the following three key roles: splitting the beam from a single cathode into 32 X 32 beams, converging the 32 X 32 beams, and blanking them individually. Accordingly, the inspection of all beams formed by the MSM is essential for the feasibility study of the system. The testing apparatus was therefore designed for measuring all the beams formed by the MSM without demagnifying them. To maintain the accuracy during the inspection of all 32 X 32 beams, the measurement process was automated. This testing apparatus was used to measure the diameters and misalignments of all beams formed by a prototype MSM. As a result, the mean values of the transverse and the longitudinal diameters were found to be 0.88 and 0.92 mu m, respectively. A single stigmator can cancel the difference between these two mean values. The standard deviations of the transverse and the longitudinal misalignments were found to be 0.77 and 0.55 mu m, respectively. This result demonstrates that all beams will reach the substrate without being interrupted by the blanking aperture array. Furthermore, the distribution of misalignments demonstrated that the misalignments are mainly caused by astigmatic aberration occurring in the illumination optics and that they can be decreased by a stigmator. These results will be used as basic data for designing the optical and data-handling systems of the BSA. (c) 2007 American Vacuum Society.