A semiconductor device includes a semiconductor substrate, and a nonvolatile memory cell disposed on the semiconductor substrate. The nonvolatile memory cell includes a field-effect transistor for data writing, and a field-effect transistor for data readout that is adjacent to the field-effect transistor for data writing. Each of the field-effect transistor for data writing and the field-effect transistor for data readout includes a gate insulating film formed on the semiconductor substrate, a floating gate formed on the gate insulating film, and diffusion layers configuring a source region and a drain region on respective sides of the floating gate viewed in the thickness direction of the semiconductor substrate. The thickness of the gate insulating film of the field-effect transistor for data readout, and the thickness of the gate insulating film of the field-effect transistor for data writing, are different.