In this paper, a substrate removing technique in a silicon Mach–Zehnder modulator (MZM) is proposed and demonstrated to improve modulation bandwidth. Based on the novel and optimized traveling wave electrodes, the electrode transmission loss is reduced, and the electro-optical group index and 50Ω impedance matching are improved, simultaneously. A 2 mm long substrate removed silicon MZM with the measured and extrapolated 3 dB electro-optical bandwidth of >50GHz and 60 GHz at the 8V bias voltage is designed and fabricated. Open optical eye diagrams of up to 90GBaud/s NRZ and 56GBaud/s four-level pulse amplitude modulation (PAM-4) are experimentally obtained without additional optical or digital compensations. Based on this silicon MZM, the performance in a short-reach transmission system is further investigated. Single-lane 112Gb/s and 128Gb/s transmissions over different distances of 1 km, 2 km, and 10 km are experimentally achieved based on this high-speed silicon MZM.