The invention is directed to an improvement of reliability in a chip-size package type semiconductor device and a manufacturing method thereof. A semiconductor substrate formed with a pad electrode is prepared, and a first protection layer formed of epoxy resin is formed on a front surface of the semiconductor substrate. Then, a via hole is formed from a back surface of the semiconductor substrate to the pad electrode. A wiring layer is then formed from the via hole of the semiconductor substrate, being electrically connected with the pad electrode through the via hole. Then, a second protection layer and a conductive terminal are formed, and the semiconductor substrate is separated into individual semiconductor dies by dicing.