Charging phenomena of a mask material during electron beam exposure are analyzed in an electron beam projection lithography system. First, the three-dimensional charge deposition distribution by the electron beam irradiation is obtained. Next, in every time step, the distributions of the accumulated charge and the potential are obtained considering the current flow due to the diffusion and the drift. As a narrow bridge pattern defined in a 5 μm × 5 μm area is assumed to lay out all over the field of 1 mm × 1 mm and the potential is grounded at the circumference of the field (1 mm × 1 mm × 1 mm), the saturated potential distribution is obtained at the central 5 μm × 5 μm area in the field. The maximum potential attained is around 4.23 μV at the center of the bridge, if the accelerating voltage of the electron beam is 100 kV, the current density is 10 A/cm2, and the material of the mask is the intrinsic Si. The contribution of the charging may be negligible to the electron beam with such a high accelerating voltage, which is going through the opening beside the bridge pattern in the projection lithography.