Amorphous SiC_x (x≤0.85) films thicker than 1μm were prepared by a magnetron-type reactive sputtering using a Si target and CH₄ gas. Microhardness (H_v), internal stress and adhesion strength by the scratch test were measured. The microhardness of SiC_0.85 films prepared by this technique was intrinsically determined to be 22GPa for 6μm-thick specimens. The microhardness for 1μm-thick SiC_x films also showed a relatively small increase with the carbon content to that for 6μm-thick SiC_x films. Compressive stresses (<3.2GPa) were observed in all SiC_x films obtained in this work. The internal stress in the SiC_x films (0.2μm thick) was well correlated with the crack length induced with a Vickers indenter as a result of the thin-layer surface stress analysis. The critical load of the SiC_x films (1μm thick) decreased with increasing internal stress.