PURPOSE: To obtain a compound semiconductor device with good yield having stable characteristics by providing active regions with different impurity concentrations on a semiinsulating substrate surface through alignment to a sheet of photo-mask.

CONSTITUTION: Windows 25a, 25b are opened in an SiO2 22 on a semiinsulated substrate GaAs with a resist mask 23 and Si ion is implanted thereto, thereby forming layers 26'a and 26'b. The mask 23 is removed, and a resist mask 28 having a window 27 which exposes the window 25b is formed. Then, Si ion is implanted again to the layer 27'b. Thereby, the layer 29' of which concentration is about two times of the layer 26'a is formed. The resist 28 and SiO2 22 are removed and the surface is covered with a protection film and then activated. This protection film is removed and the source electrode 30 and drain electrode 31 of the AuGe/Au are formed as specified on the N layer 26, while the electrode 32 on the N layer 29 through alignment with a sheet of photo-mask, and the Schottky electrodes 33, 34 of Ti/Pt/Au on the layers 26, 29 respectively through alignment thereto. Thereby, an FETSBD element having different performance can be completed. According to this structure, the characteristics are constant and yield is also good.