Disclosed is a semiconductor device and a manufacturing method, comprising: forming a pad oxide layer and a silicon nitride layer on a substrate; etching the silicon nitride layer into a plurality of segments; forming an oxide layer, having an up-and-down wave shape, by performing a traditional thermal growth field oxygen method on the semiconductor device by use of the plurality of segments serving as forming-assisted structures; performing traditional processes on the semiconductor device having an up-and-down wavy semiconductor surface, to form a gate oxide layer, a polysilicon layer, and to form a source region and a drain region by implantation The semiconductor device having an up-and-down wavy channel region may be formed by a traditional thermal growth field oxygen method, thus the manufacturing processes are simple, the cost is low, and the completed device may have a larger effective channel width and a lower on-state resistance.