A new cell was developed to study the behavior of powders during axial compaction at temperatures up to 950 K and pressures up to 1 GPa. Electrical conductivity of the sample is measured by impedance spectroscopy. Change of sample volume can be simultaneously monitored using linear variable differential transducers. Flushing with gases allows pre-conditioning of material surfaces before compaction. The cell was tested with two different grain size fractions (60–150 μm and 200–250 μm) of lithium trisilicate glass in the brittle deformation range (315 K) and in the partially plastic deformation range (ca. 660 K). The DC conductivity increases linearly with pressure up to 750 MPa at about 660 K. Lower conductivity for the smaller grain size fraction under these conditions is attributed to higher shares of pores between the grains, acting as resistors.