The lateral double-diffused MOS transistor includes a drift region of a first conductive type provided on a semiconductor substrate of a second conductive type, and a body diffusion region of the second conductive type formed on the surface within the drift region. The MOS transistor includes a gate electrode formed in such a position as it covers from part of the body diffusion region to part of the drift region located outside the diffusion region via an insulating film. The MOS transistor further includes a source diffusion region of the first conductive type and a drain diffusion region of the first conductive type formed on top of the body diffusion region and top of the drift region, respectively, both of which correspond to both sides of the gate electrode. The drain diffusion region includes a deep diffusion portion which has a 1/1000 or more concentration of a peak concentration of the source diffusion region and which is positioned deeper than the source diffusion region.