A multichip module includes a package substrate, a first semiconductor device, a second semiconductor device and a conductive bump. The first semiconductor device is flip-chip bonded to the package substrate. The first semiconductor device includes a first chip pad on a surface thereof. The second semiconductor device is mounted on the first semiconductor device. The second semiconductor device includes a second chip pad facing the first chip pad. The conductive bump connects the first chip pad to the second chip pad. The conductive bump includes a first metallic body that has a first diffusion rate and a second metallic body that has a second diffusion rate lower than the first diffusion rate.