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Modern complex drilling systems contain communication nodes like sensors, actuators, and controllers, spread along the lower end of a drill string. Here, temperatures of more than 150 °C and pressure levels up to 200 MPa are present. These environmental conditions and mechanical shocks, are extremely challenging for the reliable use of electronic components. A powerline communication system is designed and evaluated to establish a robust communication channel with low amounts of wiring. This system can operate on highly distorted physical transmission channels by adding redundancy at the sender that can then be used to correct errors at the receiver. In order to synchronize the real-time clocks among different powerline stations, a new preamble extension approach that enables precise time synchronization between multiple bus nodes is added. After design and verification, this system was manufactured in XFAB 180 nm Silicon-On-Insulator (SOI) technology allowing operating temperatures of up to 175 °C. The die size is 5.25 mm × 5.25 mm and contains a complete HomePlug 1.0 communication stack with an environment for boot, interfacing, and debugging. Its data rate reaches 6.1 Mbit/s using the fastest transmission mode and the theoretical maximum of 0.55 Mbit/s in the robust OFDM (ROBO) mode, which is of particular interest for harsh environment applications. After verifying the fabricated die, a Printed Circuit Board (PCB) for climate chamber evaluation was designed and fitted. Measurements in this chamber carried out a maximum ambient temperature of 190 °C for communication with a minimum self-heating of the die of 20 °C measured at room temperature. In combination, this is 35 °C above the specification of the technology process. The timing synchronization evaluation showed a precision of 55.6 ns over the temperature range from -30 °C to 185 °C, which is as low as 1.5 clock cycles. Power measurements of up to 190 °C have shown an average power consumption increase of only 63μW/K below 150 °C and a maximum increase of 394μW/K above 150 °C. To the best of the authors’ knowledge, this is the first high-temperature evaluation of a powerline communication ASIC, which is particularly designed for a drilling system's harsh environment.