In a monolithic MJ solar cell the subcells are interconnected by tunnel diodes. Simulations using the program DESSIS might help to understand and to improve the performance of tunnel diodes. In this work we have investigated the capability of the Hurkx model for the numerical modelling of a tunnel diode. Parameters of the Hurkx model were carefully varied. However, so far experimentally obtained IV curves of a tunnel diode could not be verified by the simulations