According to an embodiment, a method of manufacturing a semiconductor device includes forming a first modified zone in a wafer by irradiating the wafer with a laser having transmissivity with respect to the wafer along a part of a dicing line on the wafer, and forming a second modified zone in the wafer by irradiating the wafer with the laser along the dicing line on the wafer. The first modified zone is partially formed between a surface of the wafer and the second modified zone, a semiconductor interconnect layer being formed on the surface of the wafer.