In a trench MOS gate structure of a semiconductor device where trenches (T) are located between an n-type base layer (1) and an n-type source layer (3), a p-type channel layer (12) is formed adjacent to side walls of the trenches, having an even concentration distribution along a depthwise dimension of the trenches. The p-type channel layer enables saturation current to decrease without a raise of ON-resistance of the device, and resultantly a durability against short-circuit can be enhanced. The n-type source layer formed adjacent to the side walls of the trench also further enhances the durability against short-circuit. Providing contacts of the emitter electrode (7) with the n-type source layer at the side walls of the trenches permits a miniaturization of the device and a reduction of the ON-resistance as well.