SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To make thin the gate insulating film without lowering withstand voltage of gate by providing a field relaxing part at the end part of a trench gate structure where a gate conductor layer is provided at a trench part extending in the major surface of a semiconductor substrate. SOLUTION: A trench gate 4 is provided at a trench part extending in the major surface of a semiconductor substrate and reaching an N type layer 2 through a gate oxide, i.e., a silicon oxide 5, and an N+ layer 6 formed o the periphery of the trench gate 4 at the surface layer part on the major surface of the semiconductor substrate serves as a source. Each trench gate 4 is terminated in the vicinity of the outer circumferential part of a semiconductor chip and connected with a gate take-out line 7 on the major surface of the semiconductor substrate at the termination. Furthermore, a field relaxing part 8 extending along the outer circumferential part of a semiconductor chip is provided in the semiconductor substrate and connected with the termination of the trench gate 4. The field relaxing part 8 is formed into a rectangular ring surrounding a region for forming an MISFET with a curvature being provided at the corner in order to prevent concentration of field.