Method of manufacturing semiconductor device

A method of manufacturing a semiconductor device comprising:

• injecting an inert element or electron beam into a GaN-based semiconductor substrate;
• implanting magnesium into the GaN-based semiconductor substrate;
• and
• performing a heat treatment on the GaN-based semiconductor substrate after the injecting and the implanting, wherein
• a first implantation range, which is an injection range of inert element or electron beam, and a second implantation range, which is an implantation range of magnesium, overlap with each other on a surface of the GaN-based semiconductor substrate,
• a reference depth Dref (nm) calculated using a formula of Dref=D1+140 and a deepest injection depth D1 (nm) in the injecting is deeper than a deepest implantation depth D2 (nm) in the implanting,
• after the heat treatment, a concentration of magnesium decreases toward a deeper side at a predetermined decrease rate at a position of the reference depth Dref in a distribution of magnesium concentration in a depth direction within a range where the first implantation range and the second implantation range overlap with each other,
• the predetermined decrease rate is smaller than a decrease rate at which a concentration of magnesium becomes 1/10 per depth of 300 nm,
• the method of manufacturing the semiconductor device further comprises forming a gate electrode, after the heat treatment, such that a region of the surface outside the second implantation range and inside the first implantation range becomes a channel region, and
• a concentration of magnesium in the channel region is 10% or more of a concentration of magnesium in a region where magnesium is implanted in the implanting.