Abstract: Practice of this disclosure obtains a measure of the dose or fluence of implanted ions into a target for device fabrication by monitoring emitted X-rays. Illustratively, ion beams of B.sup.+, P.sup.+ or As.sup.+ have been implanted into Si over the ion energy range of 20 KeV to 2800 KeV and the data of counts of emitted X-rays has been correlated with both the solid angle intercepted by the counter and the charge intercepted by the target. In particular, the low energy soft Si(L) X-rays at 136A have been discovered for the practice of this disclosure to be very intense. The principles of this disclosure are especially applicable for very low ion doses, i.e. .ltorsim. 10.sup.12 /cm.sup.2 where charge integration is not feasible; and for neutral beam implantation with currents above about 2 milliamperes. Reproducible semiconductor devices can be fabricated by practice of this disclosure, i.e., with substantially reproducible operational characteristics, e.g.