Semiconductor device, power supply circuit, and computer

A semiconductor device comprising:

• a first nitride semiconductor layer;
• a second nitride semiconductor layer provided on the first nitride semiconductor layer and having a larger bandgap than the first nitride semiconductor layer;
• a first electrode provided on the second nitride semiconductor layer;
• a second electrode provided on the second nitride semiconductor layer;
• a gate electrode provided between the first electrode and the second electrode;
• and
• a first insulating layer provided at least between the gate electrode and the second electrode, the first insulating layer provided on the second nitride semiconductor layer, the first insulating layer being an oxide of at least one first element selected from the group consisting of hafnium (Hf), zirconium (Zr), and titanium (Ti), and containing 5×1019 cm−3 or more of at least one second element selected from the group consisting of fluorine (F), hydrogen (H), deuterium (D), vanadium (V), niobium (Nb), and tantalum (Ta), and 5×1019 cm−3 or more of at least one third element selected from the group consisting of nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), yttrium (Y), and lanthanoids (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).