A method for manufacturing a semiconductor device having a cooling mechanism comprises a modified region forming step of converging a laser light at a sheet-like object to be processed made of silicon so as to form a modified region within the object along a line to form a modified region, an etching step of anisotropically etching the object after the modified region forming step so as to advance the etching selectively along the first modified region and form a flow path for circulating a coolant as a cooling mechanism within the object, and a functional device forming step of forming a functional device on one main face side of the object.