Recent efforts at Teledyne Energy Systems, Inc. have lead to significant improvements in thermoelectric (TE) materials and power conversion devices. A number of improved formulations have been identified for standard n-type PbTe and p-type TAGS alloys. The preliminary test results appear to show nearly a 50% increase in the dimensionless figure-of-merit, ZT, for these two alloys. The new TE material formulations also exhibit a lower sublimation rate which is likely to allow use of these materials at higher heat source temperatures and thus result in higher Carnot efficiencies. The combination of higher ZT and higher Carnot efficiency allows achievement of exceptionally high thermoelectric conversion efficiencies through small changes to proven technology. For example, a thermoelectric conversion device which uses segmented BiTe/modified PbTe/modified TAGS thermoelectric couple design and operates between 300 °K and 900 °K will have a conversion efficiency of approximately 16.2%. Effort is continuing to confirm the preliminary test results and validate the materials fabrication processes. A number of improvements have also been made in the TE device fabrication processes and assembly techniques which have reduced the internal thermal and electrical losses, increased conversion efficiency, enhanced reliability and reduced manufacturing cost for the thermoelectric devices.