We present a high-power and narrow-linewidth laser for intercombination magneto-optical trapping of ytterbium (Yb) atoms using the 6s(2) S-1(0)-6s6p P-3(1) transition. The system generates 415 mW of continuous wave laser radiation at 556 nm with a linewidth of less than 100 kHz. It is based on a commercial 1W fiber laser with a frequency doubling stage. Up to 58% frequency doubling efficiency is obtained at an input power of 0.5W by using a lithium triborate crystal as a nonlinear medium. The system has been successfully used for laser cooling of Yb atoms.