Dependence of amplification A of the tunnel current in the electrochemical bridged tunneling contact on the bias voltage V, reorganization free energy E-r, intensity of Debye screening in the tunneling gap and the asymmetry parameter d is studied. The non-adiabatic electron tunneling through a one-level redox molecule is considered within the wide-band approximation for the electronic structure of the working electrodes. It is shown that, in the limit of the full Debye screening, amplification increases monotonously with the increase of V and approaches rather large limiting value A(lim) which, in its turn, increases with the increase of E-r and d. In the realistic case of the intermediate Debye screening amplification increases at first with the increase of V, then reaches a maximum A(max) at some value V-max and, when V farther increase, decreases to A = 1. The functions A(V) are calculated for different values of the parameter of the tunneling contact and it is shown that A(max) increases with the increase of E-r, d and the intensity of Debye screening. The approximate analytical expressions for A(max) and V-max which show in the explicit form their dependence on the parameters of the system are presented. (C) 2015 Elsevier Ltd. All rights reserved.