The formation of a triangular lattice of the topological spin textures (skyrmions) is suggested by recent neutron scattering studies on B20-type helical magnets. We have observed the real-space image of the skyrmion lattice in Fe0.5Co0.5Si by Lorentz transmission electron microscopy. Besides the perfect hexagonal arrangement of skyrmions, we have observed the disordered or isolated skyrmions as well as the coexistence with helical spin order. Furthermore, we have found that the skyrmion lattice is quite stable over a wide temperature region in a thin crystal plate with its thickness smaller than the skyrmion lattice constant.
