A general approach to the numerical analysis of noise in physics-based semiconductor devices is proposed. This approach is based on the Riesz representation theorem and can be applied to most partial-differential-equation-based semiconductor device models. Explicit expressions of Green’s functions for both open-circuit and short-circuit configurations are provided. Our approach is conceptually simpler than Branin’s method developed through the network analogy and it is flexible in the sense that it can be applied to any network configuration without additional matrix transformations. Numerical results of the noise in short-channel metal-oxide-semiconductor field-effect transistors and 4H-Si metal-semiconductor field-effect transistors are presented and discussed.