A semiconductor device for performing photoelectric conversion of incident light includes a substrate and a well region having different conductivity types. A depletion layer is generated in a vicinity of a junction interface between the substrate and the well region. A first trench has a depth equal to a height up to a top portion of the depletion layer generated on a bottom side of the well region and a width extending to a heavily doped region formed in the well region. A second trench has a depth larger than that of a portion of the depletion layer generated on the bottom side of the well region and a width larger than that of portions of the depletion layer generated on the sides of the well region. The second trench surrounds the first trench so as to confine the depletion layer under the first trench except for a region thereof under the heavily doped region. An insulator is buried into each the first trench and the second trench.