To provide a structure for improving resisting pressure in a vertical semiconductor device such as power MOS-FET and an IGBT element, and to provide a manufacturing method of the device.

The vertical semiconductor device such as MOS-FET and the IGBT element has the structure where gate wiring is selectively formed on a main face of a drain region through a source electrode and an insulating layer as an opposite electrode. A mask for forming a source region is corrected, and a diffusion layer for maintaining resisting pressure is formed in a drift layer just below gate wiring in an island shape by diffusion in the same process as source formation. Extension is suppressed in a depletion layer to a source electrode direction of the drift layer. Resisting pressure deterioration is improved in concentration of an electric field, and resisting pressure is improved.