This letter reports the design of terahertz amplifiers using the concept of maximum achievable gain (G(max)) of a transistor embedded in a linear, lossless, reciprocal network. Implemented in a 65-nm CMOS, by adopting the optimized G(max)-core, 280-and 300-GHz amplifiers achieve peak gain of 12 and 9 dB, peak power-added efficiency (PAE) of 1.6% and 1.4%, and gain per stage of 4 and 3 dB, respectively, while dissipating 17.9 mW, which is the best performance up to date in terms of operating frequency, gain per stage, and PAE in CMOS process.