In this paper monolithically integrated IMPATT diodes are presented. To prove the concept of completely monolithic integration, no special heatsinks or other constructions to optimize cooling were used. The diodes were grown with molecular beam epitaxy on a high resistivity silicon substrate. S-Parameter measurements were performed from 85 GHz up to 110 GHz, showing high negative impedances above the avalanche frequency. Oscillations at a frequency near 93 GHz were observed with the designed resonator circuit.