Nitride semiconductor device with a vertical channel and method for producing the nitride semiconductor device

A method for producing a nitride semiconductor device, comprising the steps of:

• forming an insulating layer having an aperture partially exposing a principle plane of a semiconductor base layer on the principle plane, defined by an m-plane or an a-plane, of the semiconductor base layer made of a conductive group III nitride semiconductor;
• forming a nitride semiconductor multilayer structure portion on a region extending onto the insulating layer from the aperture, the nitride semiconductor multilayer structure portion having a surface that includes a parallel surface parallel to the principle plane of the semiconductor base layer, and a +c-axis side first inclined surface and a −c-axis side second inclined surface inclined with respect to the principal plane of the semiconductor base layer, the nitride semiconductor multilayer structure portion including two types of group III nitride semiconductor layers each having different lattice constants;
• forming a gate electrode to be opposed to the second inclined surface;
• forming a source electrode to be electrically connected with the group III nitride semiconductor layers;
• and
• forming a drain electrode on a back surface of the semiconductor base layer opposite to the principal plane.