Abstract: A semiconductor device having a multi-value memory including an offset ROM and a manufacturing method thereof can be obtained which allows accurate formation of a source/drain region and an offset region. In this semiconductor device, an offset source/drain region is provided so that a side end portion thereof is positioned substantially in flush with a lower end of an external surface of a sidewall insulating film placed on a side surface of a first gate electrode. Consequently, the offset source/drain region can be formed easily in a self-aligned manner by ion implantation using the sidewall insulating film as a mask, thereby forming the offset region accurately in a self-aligned manner.