In the above paper,’ Higa attempted to explain nonlinear conduction in metal contacts by appealing to electron-tunneling theory. He interpreted the sublinear slope (d31/dV3 < 0) of his current-voltage plot for an aluminum-toaluminum contact on the basis of tunneling through a 4 to 7.5 A aluminumaxide film. Such an interpretation is unsatisfactory. His conclusions are based upon equations for electron tunneling that are incorrect when used to calculate nonlinear effects across ultrathin gaps. For some parameters, these equations predict sublinear tunneling currents only because they have been inconsistently expanded. As a result, these -equations predict nonphysical results when used for extreme values. Higa’s (17), except for a factor of 4, was originally given by Holm [ 11 who described it as approximate. Forlani and Minnaja [2] have shown this equation to be equivalent to the lowest order expandon in (A lp:I2)-’, although higher order terms are implicitly included in the exponentials. In Higa’s notation, A is proportional to oxide thickness and L~O is the interface work function. Simmons (31 expanded the exponentials of the Holm equation to third order in the applied voltage and retained coefficients to third order in (A ppbI2)-l. He thereby saved terms of the same order as terms previously discarded. This expansion constitutes Higa’s (18). To obtain a consistent result, we will expand Forlani and Minnaja’s [2, eq. (18)]. This equation neglects the effect of a f~te Fermi energy and also contains three typographical errors. The result for a symmetric barrier is very simply given in Higa’s notation as This equation is correct to fourth order in V and all orders of (A lph12)-’ resulting from the usual expansion of the WKB exponential. Each coefficient of this equation is necessarily positive, thus guaranteeing superlinear behavior. Hence tunneling mot be used to explain Higa’s experiment. It is difficult to comment on Higa’s experiment because of a lack of details. Such experiments do need to be satisfactorily explained to better understand the contact problem. We suggest that possible explanations of his observed sublinear behavior may be a) temperature dependent conductivity in narrow contact filaments, [4] b) space charge effects (either in the oxide or included voids) or c) charge buildup in the metal filaments due to current variations on the scale of the electron mean free path. A possible cause of the wideband noise may be the already observed [SI dielectric breakdown or electroforming in relatively thick oxide films.