Solving discrete optimization problems with genetic algorithms is in many aspects different from the solution of continuous problems. The blindness of the algorithm during the search in the space of encodings must be abandoned, because this space is discrete and the search has to reach feasible points after the application of the gentic operators. This can be achieved by the use of a problem specific genotype encoding, and hybrid, knowledge based techniques, which support the algorithm during the creation of the initial individuals and the following optimization process. In this paper a genetic algorithm for the layout generation of VLSI-chips is presented, which optimizes two, usually consecutively solved tasks simultaneously: together with the placement of the modules, the routes for the interconnection nets are optimized.