This invention improves reliability of a semiconductor device and a manufacturing method thereof. A glass substrate is bonded on a surface of a silicon wafer formed with pad electrodes. Next, via holes are formed from a back surface of the silicon wafer to pad electrodes, and a groove is formed extending along a center line of a dicing line and penetrating the silicon wafer from its back surface. After then, in processes including heating treatment, cushioning pads, wirings, a solder mask, and solder balls are formed on the back surface of the silicon wafer. Finally, the silicon wafer bolstered by the glass substrate is separated into individual silicon dice by dicing.