A high power and wide tuning range CMOS-only transmitter (TX), composed of a VCO and a power amplifier, operating from -40°C to 125°C for 76-81GHz automotive radar is presented, and for the first time, demonstrates the feasibility of CMOS technology for automotive radar across the full automotive operating temperature range. Using a foundry-based 65nm bulk technology, high output power of 13.5dBm at 27°C and 10dBm at 125°C is demonstrated with a 1V supply. Output power variation across the operating temperature is about 4dB. It is achieved by merging two sets of transmission-line-based power matching network together for power combining at a single-ended output. A cross-coupled VCO together with a frequency doubler is used to provide more than 10GHz tuning range to cover process-voltage-temperature (PVT) variations. The 77GHz phase noise at the output is -87dBc/Hz at 1MHz offset. The overall power consumption is 420mW.