Patent ID: 6946705

Claim:
A lateral short-channel DMOS in which a first conductivity-type semiconductor region is formed, a surface of the first conductivity-type semiconductor region becoming almost completely depleted during reverse bias, the lateral short-channel DMOS comprising: the first conductivity-type semiconductor region formed in one surface of a semiconductor substrate; a second conductivity-type well formed in a surface of the first conductivity-type semiconductor region and includes a channel forming region; a first conductivity-type source region formed in a surface of the second conductivity-type well; a first conductivity-type drain region formed in the surface of the first conductivity-type semiconductor region; a gate electrode that is formed via a gate insulating film in an upper part of at least the channel forming region out of a region from the first conductivity-type source region to the first conductivity-type drain region; a first conductivity-type well formed in the surface of the first conductivity-type semiconductor region and including a concentration of first conductivity-type dopant higher than that of the first conductivity-type semiconductor region and lower than that of the first conductivity-type drain region, wherein the first conductivity-type drain region is formed in a surface of the first conductivity-type well; and a second conductivity-type diffused region that is formed in a region of the surface of the first conductivity-type semiconductor region between the first conductivity-type well and the second conductivity-type well in a floating state so as not to contact the first conductivity-type well and the second conductivity-type well.