A method for manufacturing a semiconductor device according to this specification solves the problem in the prior art that the silicon on the edge of an oxide layer in an LDMOS drift region is easily exposed and causes breakdown of an LDMOS device. The method includes: providing a semiconductor substrate comprising an LDMOS region and a CMOS region; forming a sacrificial oxide layer on the semiconductor substrate; removing the sacrificial oxide layer; forming a masking layer on the semiconductor substrate after the sacrificial oxidation treatment; using the masking layer as a mask to form an LDMOS drift region, and forming a drift region oxide layer above the drift region; and removing the masking layer. The method is applicable to a BCD process and the like.