A semiconductor substrate comprising: a substrate; a seed layer disposed on the substrate; a buffer layer disposed on the seed layer; and a plurality of first nitride semiconductor layers (30, 50) disposed on the buffer layer, wherein at least one stress control layer is included between the plurality of first nitride semiconductor layers (30, 50), the buffer layer comprises a plurality of step regions (5, 7, 9, 11, 13, 15, 17) and at least one heterogeneous region (62, 62f) disposed between two step regions (15, 17) that are adjacent to the first nitride semiconductor layer, the step regions (5, 7, 9, 11, 13, 15, 17) comprise Al x Ga (1-x) N, and x in the each step region (5, 7, 9, 11, 13, 15, 17) is different from each other, the heterogeneous region (62, 62f) comprises a nitride semiconductor material different from the step regions (5, 7, 9, 11, 13, 15, 17), an amount of Al in the heterogeneous region (62, 62f) is 0, and the heterogeneous region (62, 62f) is one of InN, InGaN and GaN, the plurality of step regions (5, 7, 9, 11, 13, 15, 17) comprises a first step region in contact with the seed layer, a second step region adjacent to the first step region, and other step regions (9, 11, 13, 15, 17) excluding the first and second step regions (5, 7), the seed layer and the plurality of step regions (5, 7, 9, 11, 13, 15, 17) comprise Al, and a difference in amounts of Al between the seed layer and the first step region is in a range of 30% to 60%, characterised in that the an amount of Al in the heterogeneous region (62, 62f) is 0, and the heterogeneous region (62, 62f) is one of InN, InGaN and GaN, and amount of Al in the second step region is smaller than the amount of Al in the first step region by 20% to 40%. a substrate; a seed layer disposed on the substrate; a buffer layer disposed on the seed layer; and a plurality of first nitride semiconductor layers (30, 50) disposed on the buffer layer, wherein at least one stress control layer is included between the plurality of first nitride semiconductor layers (30, 50), the buffer layer comprises a plurality of step regions (5, 7, 9, 11, 13, 15, 17) and at least one heterogeneous region (62, 62f) disposed between two step regions (15, 17) that are adjacent to the first nitride semiconductor layer, the step regions (5, 7, 9, 11, 13, 15, 17) comprise Al x Ga (1-x) N, and x in the each step region (5, 7, 9, 11, 13, 15, 17) is different from each other, the heterogeneous region (62, 62f) comprises a nitride semiconductor material different from the step regions (5, 7, 9, 11, 13, 15, 17), an amount of Al in the heterogeneous region (62, 62f) is 0, and the heterogeneous region (62, 62f) is one of InN, InGaN and GaN, the plurality of step regions (5, 7, 9, 11, 13, 15, 17) comprises a first step region in contact with the seed layer, a second step region adjacent to the first step region, and other step regions (9, 11, 13, 15, 17) excluding the first and second step regions (5, 7), the seed layer and the plurality of step regions (5, 7, 9, 11, 13, 15, 17) comprise Al, and a difference in amounts of Al between the seed layer and the first step region is in a range of 30% to 60%, characterised in that the an amount of Al in the heterogeneous region (62, 62f) is 0, and the heterogeneous region (62, 62f) is one of InN, InGaN and GaN, and amount of Al in the second step region is smaller than the amount of Al in the first step region by 20% to 40%.