On a silicon oxide film covering a gate electrode portion, a reflowed and polished BPSG film is formed. A second interconnection layer is formed on the BPSG film. To cover the second interconnection layer, a silicon oxide film having a thickness of at least the substantial thickness of the second interconnection layer is formed on a silicon oxide film. Thus, the planarity of the base of the interconnection layer is ensured and displacement of the interconnection layer is suppressed. Accordingly, a semiconductor device having a high degree of integration is obtained.