Neutron scattering measurements were carried out for liquid Se, liquid Te, and liquid Te50Se50. The results are discussed in the context of semiconductor-to-metal transition. As to liquid Te50Se50, the vibrational modes show a remarkable change when the semiconductor-to-metal transition occurs by temperature increase. A soft stretching mode was observed for the metallic phase and it shows the structural change; the appearance of long bonds in the metallic phase. The vibrational modes for liquid Se and liquid Te were obtained and agreed well with former works. The crossover from collective to single-particle-like regime was also observed for all liquid samples and the transition ranges (Q=4.5-8 Angstrom(-1)) are presented. The diffusive features in the low-Q region and single-particle-like properties in the high-Q region are discussed and are shown to be consistent with the results for the vibrational modes. (C) 2003 American Institute of Physics.