MOS semiconductor device with excellent drain current

Claim 1

A MOS semiconductor device, comprising: a first conductivity type silicon layer having a main surface; a gate insulating film selectively formed on said main surface of said silicon layer; a gate electrode provided on the gate insulating film; an insulating side wall formed on the side of said gate electrode; and source/drain regions formed in said silicon layer; wherein said source/drain regions comprise: a first diffusion layer of second conductivity type formed in said silicon layer; and a second diffusion layer of second conductivity type formed in said silicon layer on the outside of said first diffusion layer and having a PN-junction depth larger than that of said first diffusion layer; wherein said MOS semiconductor device further comprises a conductive layer covering at least part of said first diffusion layer and at least part of said second diffusion layer; wherein said conductive layer comprises a first part having a first thickness and a second part having a second thickness larger than said first thickness; and said first part of said conductive layer covers said at least part of said second diffusion layer.