Ultrafast infrared laser pulses at 10.6 &mgr;m as short as 600±200 fs have been produced using optical semiconductor switching. This is achieved by using GaAs damaged with a 180 keV H+dose of 1×1016cm−2as an optical–optical switch. Cross‐correlation measurements are used to obtain the pulse shapes. We find that the generated infrared reflectivity pulse widths are proportional to the H+ion dose to the power −0.4. This allows a precise control over the generated pulse durations. ©1995 American Institute of Physics.