With the rapid rollout of the 5G network, more and more millimeter-wave base stations are deployed, enabling 10x faster data-rate and ubiquitous connectivity. Though millimeter-wave bands like n261 are first-time authorized for cellular communications, operating at around always sees a constant load from the modulator during symbol switching and the power delivered to antennas 1 and 2 is always out-of-phase. Heatmaps of the signal current density in the modulator are shown for both symbols. $\sim2 -$dB modulator losses are from the non-ideal switches and transmission line. 10x higher frequencies compared with 4G LTE, throughput is still fundamentally limited by the channel bandwidth. To further improve the throughput beyond 10Gb/s, moving the carrier frequency to the sub-THz range is inevitable. Over the past ten years, fully integrated sub-THz transceivers for wireless communication are gaining more and more interest. By incorporating both baseband modulators and antennas on-chip, they offer attractive, low-cost, and less-bulky solutions to next-generation communication systems, data centers and IoT. As power generation rather than bandwidth is the bottleneck for sub-THz communication, relatively simple modulation schemes like OOK, 4-ASK, 2-FSK, and QPSK are usually adopted to avoid high power consumption and reduce losses from modulation [1]–[5]. In this paper, we present a 196GHz fully integrated transmitter utilizing a proposed low-loss BPSK modulator. Benefitting from efficient fundamental oscillators, the fabricated prototype consumes only 25mW with a 1.25V supply and realizes energy efficiency per bit of 1.25pJ/bit and energy efficiency per bit per cm of 0.15pJ/bit/cm. Both metrics are the best-in-class and are at least 7x more efficient than all other sub-THz fully integrated wireless transmitters.