An organic semiconductor device includes organic semiconductor layers (3, 4) and an electron injecting electrode (5) which is composed of MgAu alloy and injects electrons into the organic semiconductor layers (3, 4). The MgAu alloy forming the electron injecting electrode (5) may contain not more than 85 atom % of Au. The organic semiconductor device may further include a hole injecting electrode (2) for injecting holes into the organic semiconductor layers (3, 4). The electron injecting electrode and the hole injecting electrode are arranged apart from each other in such a manner that they fit to each other. The organic semiconductor device may further include a gate electrode which is arranged opposite, via an insulating film, to the region between the electron injecting electrode and the hole injecting electrode.