This technology relates to high electron mobility transistors (HEMT). In conventional off-type HEMTs, a large amount of gate threshold voltage variation is often found. Transistors according to this technology include a p-type region, a barrier region, an insulation film, a gate electrode, and a channel region. The channel region is connected to an upper surface of the p-type region. The channel region is n-type or i-type and provided with a first channel region and a second channel region. The barrier region is forming a hetero-junction with an upper surface of the first channel region. The insulation film is connected to an upper surface of the second channel region and an upper surface of the barrier region. The gate electrode faces the second channel region and the barrier region via the insulation film. The first channel region and the second channel region are arranged in series in a current pathway. The transistor is turned off by completely depleting the second channel region, so the gate threshold voltage is determined by primary factors other than the density of the 2DEG of the first channel. Because the density of a 2DEG having a large amount of variation does not affect the gate threshold voltage, the amount of variation in the gate threshold voltage of this transistor is small.