In the first aspect of the present disclosure, there is provided a method of manufacturing a semiconductor device, including the steps of: providing a substrate; mounting a semiconductor die having a first die surface and a second die surface opposite to the first die surface, with the first die surface mounted to the substrate; mounting a spacer having a first spacer surface and a second spacer surface opposite to the first spacer surface, with the first spacer surface mounted on the second die surface; fusing bonding to the second spacer surface by using ultrasonic fusing.