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
; Peking Univ, Dept Phys, Beijing 100871, Peoples R China
The mass spectrum and binding radii of heavy-quark bound states are analyzed in terms of the reduced Bethe-Salpeter equation. The critical values of screening masses for and bound states at finite temperature are obtained and compared with the previous results given by nonrelativistic models.