Semiconductor device and manufacturing method thereof

On an n-semiconductor substrate (1), a trench to be a second side wall (7) is formed by cutting the substrate by means of a dicing blade having an inverted trapezoid shape. A p-diffusion layer (4) is prevented from being cut, by bringing the bottom section of the trench into contact with the p-diffusion layer (4) formed on a first main surface (2) (front surface) of the n-semiconductor substrate (1). Then, on the second side wall (7), a p-isolating layer (9) connected with a p-collector layer (8) and the p-diffusion layer (4) is formed. Since the p-diffusion layer (4) is not cut, a glass supporting substrate which supports a wafer and an expensive adhesive are eliminated, and the p-isolating layer (4) can be formed at low cost.