Density measurements for liquid Se 60Te 40, Se 80Te 20 and Se 90Te 90 were carried out at temperatures up to 1600°C and pressures up to 800 bar. The measurements were performed by means of X-ray absorption using a high-pressure vessel and a sapphire cell of the authors' own design. A distinct density variation was observed for each mixture. The thermal expansion coefficient, α, becomes negative in a certain temperature region for liquid Se 60Te 40 and Se 80Te 20 when the semiconductor-metal transition occurs. For liquid Se 90Te 10, α remains positive in the low pressure region below about 600 bar, but a temperature range which results in negative α appears at higher pressures.