In an effort to improve the insensitive munition (IM) response but maintain performance of aluminized formulations, silicon was investigated as a possible replacement for aluminum. An RDX-based silicon explosive was developed in which nearly 90% reaction of silicon to silicon dioxide was realized by 7 volume expansions as measured by the 2.54cm diameter copper cylinder expansion test. In spite of the low nitramine loading in the formulation (79wt.-%), the corresponding Gurney constant for the explosive was 2.81 +/- 0.02kms(-1), which is superior to Composition A-3 under the same experimental conditions (91% RDX, 2.69 +/- 0.02kms(-1)). Energy calculations from detonation calorimetry also indicate reaction of the silicon, which was further confirmed by both silicon metal and silicon dioxide in the analyzed residue. The energy release, despite it being equivalent to a highly loaded explosive, was found to lag behind the rate of A-3. This indicates silicon oxidation may occur sometime after lighter gas reactions in the reaction front, but is fast enough to impart work in the copper cylinder test.