US Patent 7910987 Semiconductor device

A gate electrode <13> is provided to fill up a trench <300> while covering its opening. Assuming that WG represents the diameter (sectional width) of a head portion of the gate electrode <13> located upward beyond a P-type base layer <4> and an N+-type emitter diffusion layer <51>, WT represents the diameter (sectional width) of an inner wall of a linearly extending portion of the trench <300> and WC represents the distance between the boundary (the inner wall of the trench 300) between a gate oxide film <11> and the P-type base layer <4> and an end surface of the gate electrode <13> located upward beyond the trench <300> in a section of the trench <300>, relation of either WG≧1.3·WT or WC≧0.2 μm holds between these dimensions.