This work has investigated the electrical and material characteristics of post-chemical mechanical planarization (CMP) methylsilsesquioxane (MSQ). Experimental results have shown that the dielectric properties of low k MSQ deteriorate after the CMP process. However, by applying H2-plasma post-treatment, the degraded characteristics can be restored to a similar state as that of a pre-CMP MSQ film. Material and electrical analyses were performed to elucidate the detailed mechanisms of H2-plasma treatment on post-CMP MSQ. H2-plasma treatment provides active hydrogen radicals to passivate the dangling bonds exposed in the MSQ after the CMP process. The hydrogen-rich passivation layer is hydrophobic and effectively prevents further moisture uptake. Therefore, a degradation-free CMP process can be achieved employing H2-Plasma treatment.