A chip stacking structure includes a first chip and a second chip. The first chip includes a surface having a first group of pads formed thereon, and the second chip includes a surface having a second group of pads formed thereon. The second group of pads is bonded onto the first group of pads to define a plurality of capillary passages extending in a same direction. The chip stacking structure further includes an underfill filling up interspaces between the first chip and the second chip. The chip stacking structure is capable of avoiding chip deformation and cracking during a bonding process.