In this worksheet, the physics of Silicon based P-N junction in thermal equilibrium is investigated. Special attention is devoted to the case where no bias voltage is applied to the junction. Poisson equation governing the electrostatic potential throughout the P-N junction is solved using two different approaches. According the first approach, the thin layer which extends on both sides of the junction is considered as depleted and Poisson equation is simplified and solved analytically. According to the second approach, a rigorous numerical resolution of Poisson equation is performed without resorting to any simplifying hypothesis. The worksheet presents a demonstration of Maple's capabilities in tackling the resolution of Poisson equation as a second order nonlinear nonhomogeneous ordinary differential equation and also in extracting, in addition to electrostatic potential, important physical quantities such as electrostatic field, negative and positive charge carriers densities, total charge as well as electric currents densities.