Data of electric transport, magnetic susceptibility, and NMR in P-doped silicon are examined to give a picture of metal-non metal transition in doped semiconductor : the metallic transition is percolation of donor clusters which have undergone local Mott transition. Experiments below 1K suggest a possibility for electrons in metallic samples to condense into new phases at very low temperatures. 1. Introduction. - In 1956 Mott (1 ) proposed a mechanism for the transition to metallic state of a hypothetical crystal consisting of hydrogen atoms. This mechanism is formulated on the basis of an idea that the Coulomb field, binding each electron around the host positive ion, is screened in a cooperative way when the lattice constant of the crystal is reduced below a critical value. This mechanism was applied to the explanation of MNM transition in doped semiconductor. However, impurity atoms in doped semiconductor are distributed in a random way, and this randomness made the problem very complicated. Rencently an improved mechanism, called Mott- Hubband-Anderson transition, was proposed by Mott (2) to take the effect of randomness into account. In this paper we examine the experiments of electric transport (3), static magnetic susceptibility (4) and NMR (5, 61 in phosphorus doped silicon with a purpose to establish a picture for the MNM transition in doped semiconductor. In addition to the MNM transition, doped semi- conductor indicates low temperature anomalies which seem to suggest that transitions to new phases occur at very low temperatures. Mentions will also be given of these phenomena in this paper.