The proposed S-band telemetry transmitter will operate in the exterior Venusian high pressure, 465?aC ambient atmosphere without being contained in a thermally protective container. The sealed, radiation-hardened, high-reliability, silicon-carbide-based transmitter uses an ambient heatsink to cool its high temperature transistors without the power, volume, and weight of auxiliary cooling. An innovative circuit architecture requires only one SiC semiconductor device per module; other components are ceramic or temperature-compensated machined metal parts. Operating life on Venus is limited only by the external power source; several months is anticipated. The fault-tolerant modular transmitter!|s 150 watt RF output power will support a direct Venus-Earth 8 kbps communications link. This same design solution can also be applied to very cold Titan-like applications as well. The Phase II effort culminates with a 30 day Venus life test simulation of a full scale deliverable prototype.