NIST has been developing reference materials for calibration of secondary ion mass spectrometers for approximately 10 years. The choice of materials was not only dictated by their potential market and economic impact, but also by the availability of independent analytical methods to perform certification measurements in a traceable manner. For these reasons, a decision was made to target materials of use to the semiconductor industry that were routinely analyzed by SIMS and for which good measurement calibration was important. Specifically, a program was undertaken to produce ion implants of the common dopants boron, arsenic, and phosphorus in silicon. The retained dose of the dopants would be certified by nuclear analytical methods that were available at the NIST research reactor. The first such reference material, SRM 2137, was a @super 10@B implant in Si certified by a neutron reaction method known as neutron depth profiling. Lessons learned in this first project were incorporated into the production and certification by instrumental neutron activation analysis of a @super 75@As implant in Si, SRM 2134. NIST is currently validating certification procedures for a @super 31@P implant in Si by radiochemical neutron activation analysis. We will show examples of the level of improvement in SIMS measurements that has been achieved by use of these reference materials.