There is provided a nonvolatile semiconductor memory of an aspect of the present invention includes a semiconductor substrate, first and second isolation insulating layers provided in the semiconductor substrate, a channel region between the first and second isolation insulating layers, a gate insulating film on the channel region, a floating gate electrode on the gate insulating film, an inter-gate insulating film on the floating gate electrode, and a control gate electrode on the inter-gate insulating film, wherein the isolation insulating layer is made up of a thermal oxide film provided on a bottom surface and a side surface of a concave portion of the semiconductor substrate and an insulating film which is provided on the thermal oxide film and fills the concave portion, and a dimension of the floating gate electrode in a channel width direction is more than a dimension of the channel width.