Abstract: A semiconductor substrate has a first main surface with a plurality of trenches 5a sandwiching a region in which p and n diffusions regions 2 and 3 are formed to provide a p-n junction along the depth of the trenches. P diffusion region 2 has a doping concentration profile provided by a p dopant diffused from a sidewall surface of one trench 5a, and n diffusion region 3 has a doping concentration profile provided by an n dopant diffused from a sidewall surface of the other trench 5a. A heavily doped n+ substrate region 1 is provided at a second main surface side of p and n diffusion regions 2 and 3. A depth Ld of trench 5a from the first main surface is greater than a depth Nd of p and n diffusion regions 2, 3 from the first main surface by at least a diffusion length L of the p dopant in p diffusion region 2 or the n dopant in n diffusion region 3 in manufacturing the semiconductor device. A high withstand voltage and low ON-resistance semiconductor device can thus be obtained.