In this letter, a cooperative spectrum sensing scheme for cognitive radio networks based on genetic algorithm (GA) is proposed. The proposed scheme lies in optimizing the weighting coefficients vector used in a linear soft-decision fusion- (SDF-) based framework. The detection performance of the proposed GA-assisted SDF-based scheme is compared with the conventional SDF schemes as well as the OR-logic hard-decision fusion (HDF) scheme. The simulation results show that the proposed scheme outperforms all other schemes and can achieve higher probability of detection given the same probability of false alarm.