According to recent theoretical and experimental work, the two-dimensional interacting electron gas in a strong magnetic field can be well described in terms of composite fermions for which the net magnetic field vanishes at a filling factor 1/2. We present a semiclassical theory of a geometrical effect of composite fermions that manifests itself by a strong suppression of the current through a gated sample under application of a very small gate voltage. This is explained by the strong bending of the classical ballistic trajectories of the composite fermions by the net weak magnetic field produced by the gate voltage.