The electrical conductivity σ and thermoelectric power S of liquid As-Se mixtures (up to 40 at.% As) have been measured at high temperatures (up to 1500°C) and high pressures (up to 1200 bar). For these mixtures, broad maxima appear in both the ( ln σ/ P) T versus T and the (- ln S P) T versus T curves. The maximum temperature T m a x at which these maxima occur decreases monotonically up to 30 at.% As. Around T m a x the semiconductor-metal transition occurs, which is enhanced by applying pressure. It was found that T m a x increases as the As concentration changes from 30 to 40 at.% As. The results of EXAFS suggest a substantial change in the local atomic configuration around As atoms for 30 at.% As.