A semiconductor device with reinforced under-support structure and a method for fabricating the semiconductor device are provided, which can be used in the packaging of an MPBGA/TFBGA (Multi-Package Ball Grid Array & Thin Fine-pitch Ball Grid Array) module to help reinforce the TFBGA under-support structure therein. The proposed chip-packaging method is characterized by the provision of large-area solder pads at the corners of a solder-pad array used for TFBGA attaching application, in order to form solder bumps of a large cross section and volume during reflow process to help reinforce the TFBGA under-package structure. This feature can reinforce the TFBGA under-package structure without having to use flip-chip underfill technology, and without having to use extra large type solder balls and arrange pads into different pitches as in the prior art.