The present invention provides a technique capable of attaining an improvement in current detection accuracy in a trench gate type power MISFET equipped with a current detection circuit. Inactive cells are disposed so as to surround the periphery of a sense cell. That is, the inactive cell is provided between the sense cell and an active cell. All of the sense cell, active cell and inactive cells are respectively formed of a trench gate type power MISFET equipped with a dummy gate electrode. At this time, the depth of each trench extends through a channel forming region and is formed up to the deep inside (the neighborhood of a boundary with a semiconductor substrate) of an n-type epitaxial layer. Further, a p-type semiconductor region is provided at a lower portion of each trench. The p-type semiconductor region is formed so as to contact the semiconductor substrate.