A method of producing a Group III nitride compound semiconductor device, has the following steps of: forming an n-type layer on a substrate; forming a layer containing a light emitting layer on the n-type layer; forming a p-type layer being doped with a p-type impurity on the layer; etching at least a portion of the n-type layer and at least a portion of the layer to reveal at least a part of the n-type layer and an end surface of the layer; forming a p-electrode on a surface side of the p-type layer; forming an n-electrode on the revealed part of the n-type layer; irradiating the p-type layer with an electron beam to make resistance of the p-type layer low; and acidizing at least the revealed end surface of the layer after the electron beam irradiating step.