Due to its electrical and optical interesting properties, InGaN alloy is being intensively studied to be combined with silicon in order to achieve low-cost high-efficiency solar cell. However, a relatively thick monophasic layer of InGaN is difficult to grow due to the relaxation issue in material. This issue can be avoided by semibulk structure. In this work, we present an InGaN/Si double-junction solar cell modeled using Silvaco-ATLAS TCAD software. We have taken into account polarization effect in III-N materials. We have shown that 50% of indium is needed to ensure the current matching between the top cell and the bottom cell in 2-terminal configuration. Such high indium composition is technologically challenging to grow. Thus, we have modeled a 4-terminals solar cell with relatively low indium composition (In = 25%) where current matching is not needed. With technologically feasible structural parameters, we have shown that an efficiency near to 30% can be achieved with InGaN/Si 4-contact tandem cell.