The refractive index of pure and GeO2-doped silica glasses was measured at wavelengths from 0.4 μm to 2.1 μm, over a temperature range from 20°C to 540°C. Values for the thermal coefficient of the refractive index (about 1.2×10−5/°C at 1.3 μm) were almost identical for both glasses. The data showed that material dispersion for optical fibres increases with increasing temperature.