The optimization of powders preparation and consolidation process leads to the achievement of a high thermoelectric figure of merit (ZT=1.25 at 800°C) in an n-type silicon-germanium (SiGe) alloy hot pressed at low heating rate. It has been experimentally observed that HUP compacting conditions can preserve nanostructuring. We also investigated the effect of porosity on the thermoelectric properties. Porous samples have enhanced Seebeck coefficients and low thermal conductivity. However, the figure of merit of the bulk specimen remains better than the porous samples due to a significant degradation of electrical conductivity. Working on grain boundaries engineering to enhance charge carriers mobility seems to be a promising way in addition to limiting nanograin growth with a densification process control. © 2012 American Institute of Physics.