A fabrication method of a semiconductor device that includes trench gate structures each having a gate electrode extending in a depth-direction of an element, where first trench gate structures contribute to controlling the element and second trench gate structures do not contribute. The fabrication method includes forming the trench gate structures on a front face of a semiconductor substrate; forming on the front face, an electrode pad connected to the gate electrode of at least one trench gate structure; executing screening by applying a predetermined voltage between the electrode pad and an electrode portion having a potential other than a gate potential, to apply the predetermined voltage to gate insulator films in contact with each gate electrode connected to the electrode pad; and forming the second trench gate structures having the gate electrodes connected to the electrode pad, by short-circuiting the electrode portion to the electrode pad after executing screening.