A semiconductor device comprising: a semiconductor substrate; a plurality of drain electrodes (3a-3e), each of the drain electrodes (3a-3e) being disposed in parallel along one direction on the semiconductor substrate; a plurality of source electrodes (4a-4d), each of the source electrodes (4a-4d) being disposed in an area between corresponding adjacent two of the plurality of drain electrodes (3a-3e) on the semiconductor substrate, and being disposed in parallel along the one direction; a feed line being disposed on the semiconductor substrate, and having a band shape extending in the one direction; a plurality of gate fingers (2a-2h), each of the gate fingers (2a-2h) having a linear shape connected to the feed line and extending perpendicularly from the feed line, and being disposed in an area between two adjacent electrodes on the semiconductor substrate, one of the two adjacent electrodes being a corresponding one of the plurality of drain electrodes (3a-3e) and another one of the two adjacent electrodes being a corresponding one of the plurality of source electrodes (4a-4d); and an input line disposed in parallel with the feed line on the semiconductor substrate and extending in the one direction, wherein the semiconductor device further comprises: an air bridge (9a,9b) connecting the feed line and the input line; a plurality of open stubs (8a-8h) being disposed on the semiconductor substrate, arranged so as to correspond one-to-one to the plurality of gate fingers (2a-2h)and having a line length that eliminates a target higher harmonic wave, and each of the open stubs (8a-8h) passing under the air bridge (9a,9b) and being connected directly to the feed line such that a distance from corresponding connection points, where the plurality of open stubs (8a-8h) are connected to the feed line, to corresponding gate fingers (2a-2h) of the plurality of gate fingers (2a-2h) is equal for each gate finger (2a-2h) of the plurality of gate fingers (2a-2h). a semiconductor substrate; a plurality of drain electrodes (3a-3e), each of the drain electrodes (3a-3e) being disposed in parallel along one direction on the semiconductor substrate; a plurality of source electrodes (4a-4d), each of the source electrodes (4a-4d) being disposed in an area between corresponding adjacent two of the plurality of drain electrodes (3a-3e) on the semiconductor substrate, and being disposed in parallel along the one direction; a feed line being disposed on the semiconductor substrate, and having a band shape extending in the one direction; a plurality of gate fingers (2a-2h), each of the gate fingers (2a-2h) having a linear shape connected to the feed line and extending perpendicularly from the feed line, and being disposed in an area between two adjacent electrodes on the semiconductor substrate, one of the two adjacent electrodes being a corresponding one of the plurality of drain electrodes (3a-3e) and another one of the two adjacent electrodes being a corresponding one of the plurality of source electrodes (4a-4d); and an input line disposed in parallel with the feed line on the semiconductor substrate and extending in the one direction, wherein the semiconductor device further comprises: an air bridge (9a,9b) connecting the feed line and the input line; an input line disposed in parallel with the feed line on the semiconductor substrate and extending in the one direction, wherein the semiconductor device further comprises: an air bridge (9a,9b) connecting the feed line and the input line; a plurality of open stubs (8a-8h) being disposed on the semiconductor substrate, arranged so as to correspond one-to-one to the plurality of gate fingers (2a-2h)and having a line length that eliminates a target higher harmonic wave, and each of the open stubs (8a-8h) passing under the air bridge (9a,9b) and being connected directly to the feed line such that a distance from corresponding connection points, where the plurality of open stubs (8a-8h) are connected to the feed line, to corresponding gate fingers (2a-2h) of the plurality of gate fingers (2a-2h) is equal for each gate finger (2a-2h) of the plurality of gate fingers (2a-2h).