Secure transmission of information is an indispensable part of the government and individual activities. Quantum key distribution (QKD), ascribed to its security based on the laws of quantum mechanics, has become an urgent research task to eliminate the rapidly growing threats of the ever-evolving large-scale quantum computing. In this Letter, we propose a silicon photonics transmitter using a pass-block architecture and experimentally demonstrated its performance with a demodulation chip for high-speed distributed-phase-reference QKD. We show estimated asymptotic secret key rates of 792 kbps for coherent-one-way protocol and 940 kbps for differential-phase-shift protocol over a 20 km emulated fiber link. This work provides new levels of flexibility, to the best of our knowledge, of using silicon photonics devices to incorporate QKD into future telecommunications networks.