Abstract: A laterally diffused metal oxide semiconductor device and a preparation method thereof are disclosed. The semiconductor device includes: a substrate; a body region having a first conductivity type and formed in the substrate; a drift region, having a second conductivity type, formed in the substrate and adjacent to the body region; a field plate structure, formed on the drift region, a lower surface of an end of the field plate structure close to the body region being flush with the upper surface of the substrate, and the end of the field plate structure close to the body region also having an upwardly extending inclined surface; and a drain region, having a second conductivity type, formed in an upper layer of the drift region, and in contact with the end of the field plate structure away from the body region.