Spark plasma sintering of a p-type Si-0.795 Ge0.200B0.005 alloy has been investigated in vacuum, in the 400-1200 degrees C temperature range. The densification mechanism has been determined using isothermal and anisothermal methods. In spite of a slight material degradation for the highest sintering temperatures (occurrence of cristobalite nodules homogeneously dispersed in intergranular and intragranular positions), it is proposed that densification proceeds by grain boundary sliding accommodated most probably by silicon volume diffusion. The microstructure observation of several sintered samples using transmission electron microscopy supports the densification mechanism advanced. Because the elemental grains remain mostly equiaxe whatever the sintering conditions, a grain intercalation mechanism may be also implicated during densification.