A nonvolatile memory element which is provided with a floating gate electrode and a high withstand voltage transistor which is provided with a thick gate insulating film are formed over one substrate without increase in a driving voltage of the nonvolatile memory element. A stacked film of a first insulating film and a second insulating film is formed between an island-like semiconductor region and a floating gate electrode of the nonvolatile memory element and between an island-like semiconductor region and a gate electrode of the transistor. The first insulating film overlapping with the floating gate electrode is removed, and the insulating film between the island-like semiconductor region and the floating gate electrode is formed thinner than the gate insulating film of the transistor. The transistor includes a conductive film which is formed in the same layer as the floating gate electrode and a conductive film which is formed in the same layer as a control gate electrode, and these two conductive films are electrically connected to each other and function as the gate electrodes of the transistor.