A fluidistor of the type comprising an inlet, at least two outlets, and an intermediate passage including at least one control chamber. The transition region between the inlet and the control chamber is designed to provide unstable flow to the control chamber. This increases the amplification of the device by reducing the control energy required to switch the output from one outlet to another. The unstable flow to the control chamber is caused by wedgelike shoulder means projecting substantially perpendicular to the direction of flow at the transition region from inlet to control chamber. The wedgelike shoulder means has a small dimension in the direction of flow as compared to the dimension perpendicular to the direction of flow. The transition region from the control chamber to the outlet is also sharply defined for the same reasons.