LATERAL DOUBLE-DIFFUSED METAL-OXIDE-SEMICONUDCTOR TRANSISTOR DEVICE AND LAYOUT PATTERN FOR LDMOS TRANSISTOR DEVICE

A LDMOS transistor device includes a substrate including a first insulating structure formed therein, a gate formed on the substrate and covering a portion of the first insulating structure, a drain region and a source region formed in the substrate at two respective sides of the gate, a base region encompassing the source region, and a doped layer formed under the base region. The drain region and the source region include a first conductivity type, the base region and the doped layer include a second conductivity type, and the second conductivity type is complementary to the first conductivity type. A top of the doped layer contacts a bottom of the base region. A width of the doped layer is larger than a width of the base region.