Manufacturing method of semiconductor device

A manufacturing method of a semiconductor device includes: a semiconductor substrate including a drain, a drift making contact with a front face of the drain, a body contacting with a front face of the drift, a source provided in part of a front face of the body, and a floating surrounded by the drift; and a gate including an insulator formed on an inner wall of a trench and a electrode disposed inside the insulator and which has a bottom portion contacting with the floating, the manufacturing method includes: forming the trench in a semiconductor wafer so as to have a bottom portion in which an end portion in a short direction perpendicular to a longitudinal direction thereof is deeper than a central portion; injecting an impurity ions into the bottom portion of the trench; and forming the central portion of the trench in the short direction to be deepened.