Acad Sinica, Inst Theoret Phys, Beijing 100080, Peoples R China
; CCAST, World Lab, Beijing 100080, Peoples R China
; Acad Sinica, Inst High Energy Phys, Beijing 100039, Peoples R China
; Beijing Univ, Dept Phys, Beijing 100871, Peoples R China
; Max Planck Inst Kernphys, D-69029 Heidelberg, Germany
The mass spectra and binding radii of heavy quark bound states are studied on the basis of the reduced Bethe-Salpeter equation. The critical values of screening masses for c (c) over bar and b (b) over bar bound states at a finite temperature are obtained and compared with the previous results given by nonrelativistic models. [S0556-2813(99)01205-4].