A semiconductor device includes a semiconductor layer that has a main surface, a trench gate structure that includes a trench formed in the main surface and having a first sidewall at one side, a second sidewall at the other side and a bottom wall in a cross-sectional view, an insulation layer formed on an inner wall of the trench, and a gate electrode embedded in the trench with the insulation layer between the trench and the gate electrode and having an upper end portion positioned at a bottom-wall side with respect to the main surface, a plurality of first-conductivity-type drift regions that are respectively formed in a region at the first sidewall side of the trench and in a region at the second sidewall side of the trench such as to face each other with the trench interposed therebetween in a surface layer portion of the main surface and that are positioned in a region at the main surface side with respect to the bottom wall, and a plurality of first-conductivity-type source/drain regions that are formed in surface layer portions of the plurality of drift regions, respectively.

A method of manufacturing a semiconductor device, where the device includes a donor layer that is obtained by changing a crystal defect formed in a first-conduction-type drift layer by proton radiation into a donor and in which the donor layer has an impurity concentration distribution including a first portion with a maximum impurity concentration and a second portion with a concentration gradient in which the impurity concentration is reduced from the first portion to both surfaces of the first-conduction-type drift layer. The method includes performing proton radiation for a first-conduction-type semiconductor substrate which will be the first-conduction-type drift layer to form a crystal defect in the first-conduction-type semiconductor substrate; and performing a heat treatment at a temperature equal to or higher than 300 C. and equal to or lower than 450 for one minute to 300 minutes to change the crystal defect into a donor.

Provided are a diode, a junction field effect transistor (JFET), and a semiconductor device that have a top doped region. A dopant concentration gradient of the top doped region at one side is different from the dopant concentration gradient of the top doped region at an opposite side. The top doped region is able to increase a breakdown voltage of the device and decrease an on-state resistance (Ron) of the device.

Provided are a diode, a junction field effect transistor (JFET), and a semiconductor device that have a top doped region. A dopant concentration gradient of the top doped region at one side is different from the dopant concentration gradient of the top doped region at an opposite side. The top doped region is able to increase a breakdown voltage of the device and decrease an on-state resistance (Ron) of the device.