A semiconductor device includes: a substrate; and an n-type layer including a nitride semiconductor formed on the surface of the substrate. In the n-type layer, the concentration of donor impurities (excluding O) is 1×1015 cm−3 or more and 1×1020 cm−3 or less, the concentration of C impurities is 1×1016 cm−3 or less, the concentration of O impurities is 1×1016 cm−3 or less, the concentration of Ca impurities is 1×1016 cm−3 or less, and the sum total of the concentrations of the C impurities, the O impurities, and the Ca impurities is lower than the concentration of the donor impurities. Such a semiconductor device can be fabricated by using a halogen-free vapor phase epitaxy (HF-VPE) device.