A semiconductor device with a WLP structure that enables the improvement of heat resistance. A dam layer which spreads over a PI film and an Si substrate for a chip is formed between the Si substrate and a sealing resin so as to surround the chip on all sides. A material for the dam layer is selected so that good adhesion will be obtained between the dam layer and the Si substrate, between the dam layer and the PI film, and between the dam layer and the sealing resin. As a result, even if a crack appears at a portion on a side of the semiconductor device where the Si substrate and the sealed resin are joined in a heating environment, the crack does not run inside the dam layer. This prevents the peeling of the sealing resin or peeling inside the chip and the performance of the semiconductor device is maintained.