A line‐source electron beam annealing system has been developed for directed‐energy beam processing of materials. The electron gun in this system produces a sheet beam which is focused at the sample into a line that can be swept laterally for area annealing. The system provides well‐characterized beam dwell times in the range 5 &mgr;s–2 ms, a heretofore neglected time regime. We demonstrate line‐source annealing by the system for the case of (100) epitaxial regrowth of 1250 A˚ of amorphous As‐implanted Si with dwell times as short as 150 &mgr;s. Calculations of temperature profiles and the corresponding regrowth thicknesses for solid phase epitaxy are presented for Si as a function of beam power density and dwell time. Measured power density and dwell time thresholds for layer regrowth are consistent with solid phase epitaxy of the amorphous layer. The results show the utility of the system in exploring regrowth at temperatures near the melt.