We succeeded in the fabrication of high-J(c) ( critical current density) MgB2/Fe wires applying the internal Mg diffusion (IMD) process with a pure Mg core and SiC addition. A pure Mg rod with a diameter of 2 mm was placed at the center of a Fe tube with an outer diameter of 6 mm and an inner diameter of 4 mm, and the space between the Mg and the Fe tube was filled with B powder or a powder mixture of B-(5 mol%) SiC. The composite was cold worked into a wire with a diameter of 1.2 mm and finally heat treated at temperatures above the melting point of Mg (similar to 650 degrees C). During the heat treatment, liquid Mg infiltrated into the B layer and reacted with B to form MgB2. X-ray diffraction analysis indicated that the major phase in the reacted layer is MgB2. Scanning electron microscopy (SEM) analysis shows that the density of the MgB2 layer is higher than that of the usual powder-in-tube ( PIT) processed wires. The wires with additional 5 mol% SiC heat treated at 670 degrees C showed J(c) values higher than 105 A cm(-2) in 8 T and 41 000 A cm(-2) in 10 T at 4.2 K. These values are much higher than those of the usual PIT processed wires, even compared to those with additional SiC. The higher density of the MgB2 layer obtained by the diffusion reaction is the major cause of these excellent Jc values.