Melt growth behavior of polycrystalline silicon was observed using a newly developed in-situ monitoring system consisting of a furnace and a microscope. It is possible to perform a directional growth from seed crystal or crucible wall and to observe the growth interface by using this system. Differences of growth rate or interfacial morphology among each grain of polycrystalline silicon were observed during melt growth. The Mullins-Sekerka instability of growth interface was also observed in a silicon melt for the first time. This observation system is confirmed to become a useful tool for revealing the growth mechanism of polycrystalline silicon. (C) 2003 Elsevier B.V. All rights reserved.