Quasi-two-dimensional (213) simulation of resonant-tunneling diode is presented. 2D effects are studied both analytically and numerically. For numerical simulation, the local resonant-tunneling layer (RTL) model is implemented in 2D drift-diffusion simulator as the boundary condition for the current. It is shown that the increase of linear size of the device results in the strong decrease of peak current and increase of valley current. For the device with large current density, designed for high-frequency applications, the 2D effects appear already at linear size about 1 mum. The local model for current through RTL can be used for 2D or 3D numerical simulation of a wide variety of devices including the RTL, such as heterojunction bipolar transistor, resonant-tunneling transistor etc. (C) 2002 Elsevier Science Ltd. All rights reserved.