A method for manufacturing a semiconductor device includes forming a first semiconductor layer on a semiconductor substrate, forming a first insulator layer on the first semiconductor layer, forming a patterned second semiconductor layer on the first insulator layer, the patterned second semiconductor layer having an actual thickness greater than a target thickness and exposing a portion of the first insulator layer; forming a second insulator layer as a spacer on the exposed portion of the first insulator layer, and performing an etching process on the patterned second semiconductor layer until the second semiconductor layer has the target thickness and concurrently removing the second insulator layer. The method can eliminate capillary etching of the spacer in a subsequent removal of the first insulator layer.