Abstract: Provided are a semiconductor device and a bidirectional field effect transistor which can easily overcome the tradeoff relation between the high voltage resistance and high speed in the semiconductor device using a polarization super junction, realize both the high voltage resistance and elimination of the occurrence of current collapse, operate at a high speed, and further the loss is low. The semiconductor device comprises a polarization super junction region and a p-electrode contact region. The polarization super junction region comprises an undoped GaN layer 11, an undoped AlxGa1-xN layer 12 with a thickness not smaller than 25 nm and not larger than 47 nm and 0.17?x?0.35, an undoped GaN layer 13 and a p-type GaN layer 14. When the reduced thickness tR is defined as tR=u+v(1+w×10?18) for the thickness u [nm] of the undoped GaN layer 13, the thickness v [nm] and the Mg concentration w [cm?3] of the p-type GaN layer 14, tR?0.864/(x?0.134)+46.0 [nm] is satisfied.

Abstract: Provided is a semiconductor element in which a two-dimensional hole gas with an enough concentration can exist, even though the p-type GaN layer is not provided on the topmost surface of the polarization super junction region. The semiconductor element comprises a polarization super junction region comprising an undoped GaN layer 11 with a thickness a [nm] (a is not smaller than 10 nm and not larger than 1000 nm), an AlxGa1-xN layer 12 and an undoped GaN layer 13. The Al composition x and the thickness t [nm] of the AlxGa1-xN layer 12 satisfy the following equation t??(a)x?(a) Where ? is expressed as Log (?)=p0+p1 log (a)+p2{log (a)}2 (p0=7.3295, p1=?3.5599, p2=0.6912) and ? is expressed as ?=p?0+p?1 log (a)+p?2{log (a)}2 (p?0=?3.6509, p?1=1.9445, p?2=?0.3793).

Abstract: Provided are a semiconductor device and a bidirectional field effect transistor which can easily overcome the tradeoff relation between the high voltage resistance and high speed in the semiconductor device using a polarization super junction, realize both the high voltage resistance and elimination of the occurrence of current collapse, operate at a high speed, and further the loss is low. The semiconductor device comprises a polarization super junction region and a p-electrode contact region. The polarization super junction region comprises an undoped GaN layer 11, an undoped AlxGa1-xN layer 12 with a thickness not smaller than 25 nm and not larger than 47 nm and 0.17?x?0.35, an undoped GaN layer 13 and a p-type GaN layer 14. When the reduced thickness tR is defined as tR=u+v(1+w×10?18) for the thickness u [nm] of the undoped GaN layer 13, the thickness v [nm] and the Mg concentration w [cm?3] of the p-type GaN layer 14, tR?0.864/(x?0.134)+46.0 [nm] is satisfied.