Silicon waveguide devices based on free-carrier dispersion are key co mponents for realizing high-speed optical communications and optical interconnections.In thi s paper,the silicon waveguide device using a lateral p-i-n diode configuration is modeled.We nume rically analyze the electrical and optical properties of the silicon waveguide device.A two-dimensional simulation package,Atlas from Silvaco,is employed to simulate the steady state and transient behaviors of the lateral p-i-n diode.According to the change of the electron and hole distributions caused by an applied voltage,the induced real refractive index an d optical absorption coefficient variations produced by free-carrier dispersion at a wavelength of 1.55μm are obtained. From the values of the refractive index and optical absorption coefficient varia tions,the finite-difference (FD) method is then used for the calculation of the effective index and optical losses.Meanwhile,in order to verify the established model,a n electro-optic intensity modulator based on the Mach-Zehnder interferometer,in which phase-sh ifters are embedded with the same p-i-n diodes,is fabricated on a silicon-on-insulator (SOI) wafer by a 0.18μm standard commercial CMOS line.Our calculations indicate that this work can be used to optimize the design of silicon electro-optic device.