A semiconductor device having a semiconductor crystalline laminate structure comprising a first semiconductor layer consisting of a first alloyed semiconductor, a second semiconductor layer which has an energy gap wider than that of said first alloyed semiconductor and a lattice constant smaller than that of said first alloyed semiconductor and consists of one semiconductor selected from a group consisting of single-element semiconductor, compound semiconductor, and alloyed semiconductor, and a third semiconductor layer which consists of a second alloyed semiconductor having an energy gap wider than that of said first alloyed semiconductor and is formed between said first semiconductor layer and said second semiconductor layer and in contact with each of them, wherein a semiconductor having a largest lattice constant among semiconductors constituting said first alloyed semiconductor is included only in said first semiconductor layer and said third semiconductor layer among said first, second, and third semiconductor layers, wherein said semiconductor having a largest lattice constant is a semiconductor containing In as a constituent element, wherein the In mole fraction of said third semiconductor layer is within a range from 0.15 to 0.3, and wherein said semiconductor device is an HEMT, said first semiconductor layer is a channel, said second semiconductor layer is a carrier supply layer, and said third semiconductor layer is a spacer, said device further comprising a gate electrode overlying said channel, and source and drain electrodes respectively at opposite sides of the gate electrode.