A spectroscopic study was made of imploding shock waves in a hemispherical chamber filled with an O2‐H2‐He mixture at high pressure (∼10 atm). The waves were generated by reflecting an exploding detonation wave off the periphery of the chamber. The strong focusing of classical imploding shock waves was verified quantitatively, but the temperature of the shock‐heated gas near the origin of the chamber was found to be limited to rather low values (∼5000°K). The results generally agree well with calculations employing the artificial‐viscosity technique if it is assumed that the minimum shock radius near the origin is limited to the extent of the experimentally observed luminosity region.