We investigate the transport of electrons through a double-barrier resonant-tunneling structure in the regime where the current-voltage characteristics exhibit bistability. In this regime one of the states is metastable, and the system eventually switches from it to the stable state. We show that the mean switching time τ grows exponentially as the voltage V across the device is tuned from the boundary value V th into the bistable region. In samples of small area we find ln τ ∝ |V − V th | 3/2 , while in larger samples ln τ ∝ |V − V th |. [7]. Recent experiments [8,9] with such devices have demonstrated that near the boundary of the bistable region one of the two states is metastable, and its lifetime has been studied by measuring current as a function of time at different voltages. Thus, these devices provide an ideal experimental system for studying the decay of metastable states in real time. In this paper we develop the theory of switching times in double barrier structures, Fig. 1(a). We expect the results to be relevant for other devices in which sequential resonant tunneling plays a key role in describing the electronic transport, such as weakly-coupled superlattices.We concentrate on the case of intrinsic bistability, which can be observed by measuring current I as a function of voltage V applied to the device while the impedance of the external circuit equals zero. As shown in Ref. 6, for a certain range of bias V , two states of current I are possible at the same value of the voltage, and the I-V curve has characteristic hysteretic behavior. As one increases bias, the upper branch ends at some boundary voltage V th , shown schematically in Fig. 1(b). If the voltage V is fixed just below the threshold V th , the system stays in the upper state for a finite time τ , before decaying to the stable lower state.1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 eV EWe will show that the lifetime of the metastable state τ can be understood by analogy to the problem of a Brownian particle in a double-well potential (Fig. 2). Here the coordinate of the Brownian particle has the meaning of the current I in the device (or the electron density n). In the problem of the Brownian particle, τ depends exponentially on the height of the potential barrier U b separating the local and global minima, i.e. τ ∝ exp(U b /T * ), where T * is the temperature. Unlike a Brownian particle, a DBRTS at nonzero bias is a non-equilibrium system in which fluctuation phenomena are driven by shot noise in the current rather than the electron temperature T . On the boundary of the bistable region, the local minimum disappears, and therefore U b goes to zero. Thus, it is clear that τ will depend exponentially on the voltage measured from the boundary V th of the bistable region.Here we investigate effects of shot noise in DBRTS using the framework of the theoretical model introduced in Ref. 10. The DBRTS is formed as a layered semiconductor heterostructure. The electrostatic potential across the device is shown in Fig. 1(a). The potent...