This paper reports comparative analyses of low energy (≤50 keV) B and As implants in Si using ion microscope (Cameca IMS 3-f) and quadrupole SIMS (Perkin–Elmer Physical Electronics SIMS II) instrumentation. For B implants, the measured profiles indicate that channeling of the B during implantation is primarily responsible for the non-Gaussian distributions, rather than ion beam mixing effects. For very shallow (15 keV) As implants, the mean range and peak concentration measured by SIMS and recent RBS measurements are in reasonable agreement with the calculated distribution.