The present invention relates to a semiconductor device, a solid-state image sensor and a camera system capable of reducing the influence of noise at a connection between chips without a special circuit for communication and reducing the cost as a result. The semiconductor device includes: a first chip; and a second chip, wherein the first chip and the second chip are bonded to have a stacked structure, the first chip has a high-voltage transistor circuit mounted thereon, the second chip has mounted thereon a low-voltage transistor circuit having lower breakdown voltage than the high-voltage transistor circuit, and wiring between the first chip and the second chip is connected through a via formed in the first chip.