This letter presents a novel monolithic integrated frequency multiplier circuit for free space power generation in the W-band (75-110 GHz). The circuit is based on a submicrometer GaAs Schottky diode monolithically integrated with a slot antenna on a GaAs semi-insulating substrate. The fabricated diode with an air-bridged Schottky contact and a U-shaped ohmic contact showed an ideality factor of about 1.25 and a zero bias cutoff frequency higher than 1.25 THz. Using input signals between 15 and 50 GHz, the free space power generated in the W-band corresponding to ×2, ×3, ×4, and ×5 frequency multiplication was measured and showed minimum isotropic conversion losses (with antenna) of 11.5, 16.9, 23.7, and 26.4 dB, respectively.