A room-temperature electrical property of three-terminal ballistic junctions (TBJs) is predicted. For a symmetric TBJ, it is shown that when finite voltages V and −V are applied to the left and right branches, the voltage output Vc from the central branch will always be negative. This characteristic appears even when the symmetry in the TBJ is broken, provided that |V| is larger than a threshold. Applications of these devices in nanoelectronics are proposed.