Four-probe resistivity measurements were made on an organic semiconductor, beta'-(BFDT-TTF)(2)ICl2 up to 10 GPa by using a diamond anvil high-pressure cell. The activation energy was decreased with increasing pressure and the metallic phase appeared around 8 GPa. When the pressure was kept around 10 GPa, the resistivity was gradually increased with time, indicating an irreversible pressure-induced solid state transformation.