The fundamental transmission characteristics of KrF laser radiation (248 nm) through the step‐index‐type fused quartz fiber have been determined. For the step‐index‐type fused quartz fiber used the transmission loss is about 0.5 dB/m at power densities up to 3.9 MW/cm2and 2 dB/m at 100 MW/cm2. One of the applications of this intense UV KrF laser transmission via optical fibers is the development of a gas insulated spark‐gap switch trigger by a KrF laser through a 2‐m‐long optical fiber. As a result, at a voltage 90% of the self‐breakdown voltage and at an illumination power density of 1.2 MW/cm2, a full trigger jitter of less than 5 ns is realized and it corresponds to a 1‐&sgr; jitter of less than 1 ns. The illumination energy is as low as 10 &mgr;J/shot.