The performances of a semiconductor device are improved. A semiconductor device has a transfer transistor and a photodiode. The photodiode has an n type semiconductor region, an n+ type semiconductor region, and a second p type semiconductor region surrounded by a first p type semiconductor region of an interpixel isolation region. The n+ type semiconductor region is formed on the main surface side of the semiconductor substrate, and the n type semiconductor region is formed under the n+ type semiconductor region via the second p type semiconductor region. In the channel length direction of the transfer transistor, in the n type semiconductor region, an n−− type semiconductor region having a lower impurity density than that of the n type semiconductor region is arranged, to improve the transfer efficiency of electric charges accumulated in the photodiode.