We have developed a robust wafer-level substrate bonding process that has allowed us to bond CVD diamond to GaAs membrane-based submillimeter-wave Schottky diode frequency multipliers. The high thermal conductivity of CVD diamond allows the chip to dissipate heat more efficiently thus increasing the power handling capability of the chips. This process has resulted in single-chip multiplier devices working in the submillimeter-wave range that can handle hundreds of milliwatts of input power. Output powers of 40 mW at 250 GHz and 27 mW at 300 GHz from a single chip have been demonstrated with this method. It is expected that by power combining these chips it is now possible to achieve a wideband 300 GHz signal with more than 100 mW of power. This represents a dramatic improvement in the current state of the art and allows one to begin realizing submillimeter-wave radar applications.