Abstract: Phase-change optical switches offer low power consumption, programmability, and ease of integration, serving as core components for high-performance photonic computing chips. However, the weak coupling between phase-change materials (PCMs) and silicon waveguides necessitates larger phase change material (PCM) volumes to achieve high extinction ratios, hindering the high-density integration of switch arrays. To address this challenge, this study employs germanium-antimony-tellurium-based PCMs as the optical modulation medium and designs a high-performance silicon-based optical switch through structural optimization. By heterogeneously integrating PCMs with silicon waveguides, a high-performance device is realized. The finite-difference time-domain (FDTD) method is used to simulate and analyze the impact of strip and tapered waveguide structures on optical transmission performance. Simulation results indicate that for a PCM with dimensions of 3 μm in length and 40 nm in thickness, the strip waveguide structure achieves an extinction ratio (ER) of 21.01 dB at the 1550 nm wavelength, whereas the tapered waveguide structure attains 32.98 dB. Further analysis reveals that, compared with the strip waveguide, the tapered structure enhances the interaction between the PCM and the optical field within the waveguide, thereby improving the device extinction ratio.