We report and model the use of preannealing hydrogen treatment to improve the growth length in Au-induced lateral crystallization (MILC) of phosphorous-doped a-Si:H. Doped phosphorus atoms generate a large number of dangling bonds, which then capture metal atoms and interrupt the MILC processing, thus retarding the growth length. With the hydrogen treatment, the dangling bonds are passivated, and thus the MILC-grown polysilicon length can be increased from 18.6 to 53.9 mu m after 6 h annealing.