We report new experimental results of low temperature (4.2 K - 95 K) transport phenomena in uncompensated n-type InSb sample, where very low free carrier concentrations are obtained using the properties of a metastable impurity state. By varying free electron density in the same sample, from 1011 cm-3 to 1014 cm-3 the metal-non metal transition is observed. The evidence of an activation energy of the hydrogenic level corresponding to the effective Rydberg is given. Above 40 K the role of a donor-like impurity level is shown.