Shock temperatures of fused silica were determined using radiance intensity measurements at two color bands of 620 and 810 nm. The shock temperature increased from 2.0×103to 3.3×103K in the pressure range between 31.8 and 40.5 GPa, and up to 4.2×103K in the range up to 65.1 GPa. The rate of increase of temperature with pressure decreased at ∼40 GPa. The low gradient above 40 GPa suggests that a shock‐induced phase transformation of fused silica begins at ∼40 GPa.