The scaling of alkaline electrolysis systems is restricted by the reducing current efficiency with increasing cell number due to stray currents. This paper focuses on the design optimization of channels in alkaline stacks considering the trade-off between current efficiency and pressure drop, which enables the efficient operation of large stacks. For this purpose, two equivalent circuit models are applied to predict the current efficiency and the pressure drop. The first is used to model the stray currents and predict the current efficiency, while the latter describes the hydraulic pressure drop and hence gives valuable information to reduce the pumping power. Based on the established models, a design optimization approach is proposed to maximize the system efficiency and derive the optimal channel geometry. The results suggest that the longest channels should be used to reduce the stray current, and the channel diameters can be determined by the trade-off between current efficiency and pumping consumption. By optimizing the channel geometry, the current and system efficiency is promoted by 9.4% and 5.3% of an exemplary alkaline electrolysis system. This study also assesses the impact of cell area, current density, manifold length and maximum pressure drop, providing valuable information for system design.