The depth of melt front penetration induced byQ‐switched ruby‐laser irradiation has been measured by electron microscopy for laser pulses of different duration and energy density in silicon crystals diffused with phosphorous. In as‐diffused specimens (1100 °C 1‐h PH3source) dislocation loops and phosphorous precipitates were distributed to a depth of about 1.0 &mgr;m. The precipitates and loops were dissolved to certain depths by irradiation withQ‐switched ruby‐laser pulses. Dissolving of precipitates provides evidence for melting by the laser radiation, and the depth over which precipitates are dissolved provides a measure of the melt front penetration depth.