The silicon traveling-wave (TW) Mach-Zehnder modulator (MZM) is one of the most important devices in silicon photonic transceivers for high-speed optical interconnects. Its phase shifter utilizes carrier depletion of pn diodes for high speed, but suffers low modulation efficiency. Extensive efforts have been made on pre-fabrication optimizations, including waveguides, doping, and electrodes to enhance high-frequency modulation efficiency. Instead, we here propose an adaptive post-fabrication distributed-bias driving method that enables 20%∼30% high-frequency efficiency enhancement at both 10 and 25 Gbps without doing any optimizations for a silicon TW-MZM. This method explores the bias nonlinearity of index modulation which, to the best of our knowledge, is utilized for the first time in driving silicon modulators to improve the efficiency. We demonstrated the viability of this adaptive driving concept to achieve better performance, and this Letter could open new avenues for silicon traveling-wave modulator design and performance trade-off.