According to one embodiment, a transistor includes: a structural body; an insulating film; a control electrode; a first electrode; and a second electrode. The structural body includes a first through a third semiconductor regions, and includes a compound semiconductor having a first and a second elements. The first electrode is electrically continuous with the third semiconductor region. The second electrode is electrically continuous with the first semiconductor region. The structural body has a first region provided above a lower end of the second semiconductor region and a second region other than the first region. The first region is a region formed by making a ratio of concentration of source gas of the second element to concentration of source gas of the first element larger than 1.0. Impurity concentration of the first conductivity type in the first region is higher than that in the second region.