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In this paper, we investigate the influence of high temperature and high pressure (hot pressure) on the magnetic and transport properties of polycrystalline CrO(2) samples compacted under high pressure and high temperature of up to 5 GPa and 600 degrees C, respectively. The magnetic moment increases with compacting temperature, and a metal-semiconductor transition is observed in hot-pressed samples, different from the cold-pressed samples. These results indicate that the formation of Cr(2)O(3) at the grain boundaries of CrO(2) is suppressed by hot pressure. The magnitude of low field magnetoresistance of up to 1 T at 5 K is enhanced first with the increase of compacting temperature and then decreased under higher compacting temperature. This result can be well explained by the change of spin-dependent tunneling at the modulated grain boundaries of CrO(2) due to the transformation from Cr(2)O(3) to CrO(2) under hot pressure. (c) 2007 American Institute of Physics.